14616d0f9Sopenharmony_ci<!DOCTYPE html> 24616d0f9Sopenharmony_ci<html lang="en"> 34616d0f9Sopenharmony_ci<head> 44616d0f9Sopenharmony_ci<title>Time zone and daylight saving time data</title> 54616d0f9Sopenharmony_ci<meta charset="UTF-8"> 64616d0f9Sopenharmony_ci<style> 74616d0f9Sopenharmony_cipre {margin-left: 2em; white-space: pre-wrap;} 84616d0f9Sopenharmony_ci</style> 94616d0f9Sopenharmony_ci</head> 104616d0f9Sopenharmony_ci<body> 114616d0f9Sopenharmony_ci<h1>Time zone and daylight saving time data</h1> 124616d0f9Sopenharmony_ci<p> 134616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Time_zone">Time zone</a> and 144616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Daylight_saving_time">daylight-saving</a> 154616d0f9Sopenharmony_cirules are controlled by individual 164616d0f9Sopenharmony_cigovernments. They are sometimes changed with little notice, and their 174616d0f9Sopenharmony_cihistories and planned futures are often recorded only fitfully. Here 184616d0f9Sopenharmony_ciis a summary of attempts to organize and record relevant data in this 194616d0f9Sopenharmony_ciarea. 204616d0f9Sopenharmony_ci</p> 214616d0f9Sopenharmony_ci <h3>Outline</h3> 224616d0f9Sopenharmony_ci <nav> 234616d0f9Sopenharmony_ci <ul> 244616d0f9Sopenharmony_ci <li>The <code><abbr>tz</abbr></code> database product and process 254616d0f9Sopenharmony_ci <ul> 264616d0f9Sopenharmony_ci <li><a href="#tzdb">The <code><abbr>tz</abbr></code> database</a></li> 274616d0f9Sopenharmony_ci <li><a href="#download">Downloading the <code><abbr>tz</abbr></code> database</a></li> 284616d0f9Sopenharmony_ci <li><a href="#changes">Changes to the <code><abbr>tz</abbr></code> database</a></li> 294616d0f9Sopenharmony_ci <li><a href="#coordinating">Coordinating with governments and distributors</a></li> 304616d0f9Sopenharmony_ci <li><a href="#commentary">Commentary on the <code><abbr>tz</abbr></code> database</a></li> 314616d0f9Sopenharmony_ci </ul> 324616d0f9Sopenharmony_ci </li> 334616d0f9Sopenharmony_ci <li>Uses of the <code><abbr>tz</abbr></code> database 344616d0f9Sopenharmony_ci <ul> 354616d0f9Sopenharmony_ci <li><a href="#web">Web sites using recent versions of the <code><abbr>tz</abbr></code> database</a></li> 364616d0f9Sopenharmony_ci <li><a href="#protocols">Network protocols for <code><abbr>tz</abbr></code> data</a></li> 374616d0f9Sopenharmony_ci <li><a href="#compilers">Other <code><abbr>tz</abbr></code> compilers</a></li> 384616d0f9Sopenharmony_ci <li><a href="#TZif">Other <abbr>TZif</abbr> readers</a></li> 394616d0f9Sopenharmony_ci <li><a href="#software">Other <code><abbr>tz</abbr></code>-based time zone software</a></li> 404616d0f9Sopenharmony_ci </ul> 414616d0f9Sopenharmony_ci </li> 424616d0f9Sopenharmony_ci <li>Related data 434616d0f9Sopenharmony_ci <ul> 444616d0f9Sopenharmony_ci <li><a href="#other-dbs">Other time zone databases</a></li> 454616d0f9Sopenharmony_ci <li><a href="#maps">Maps</a></li> 464616d0f9Sopenharmony_ci <li><a href="#boundaries">Time zone boundaries</a></li> 474616d0f9Sopenharmony_ci </ul> 484616d0f9Sopenharmony_ci </li> 494616d0f9Sopenharmony_ci <li>Timekeeping concepts 504616d0f9Sopenharmony_ci <ul> 514616d0f9Sopenharmony_ci <li><a href="#civil">Civil time concepts and history</a></li> 524616d0f9Sopenharmony_ci <li><a href="#national">National histories of legal time</a></li> 534616d0f9Sopenharmony_ci <li><a href="#costs">Costs and benefits of time shifts</a></li> 544616d0f9Sopenharmony_ci <li><a href="#precision">Precision timekeeping</a></li> 554616d0f9Sopenharmony_ci <li><a href="#notation">Time notation</a></li> 564616d0f9Sopenharmony_ci </ul> 574616d0f9Sopenharmony_ci </li> 584616d0f9Sopenharmony_ci <li><a href="#see-also">See also</a></li> 594616d0f9Sopenharmony_ci </ul> 604616d0f9Sopenharmony_ci </nav> 614616d0f9Sopenharmony_ci 624616d0f9Sopenharmony_ci<section> 634616d0f9Sopenharmony_ci<h2 id="tzdb">The <code><abbr title="time zone">tz</abbr></code> database</h2> 644616d0f9Sopenharmony_ci<p> 654616d0f9Sopenharmony_ciThe <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a> 664616d0f9Sopenharmony_citime zone database contains code and data 674616d0f9Sopenharmony_cithat represent the history of local time 684616d0f9Sopenharmony_cifor many representative locations around the globe. 694616d0f9Sopenharmony_ciIt is updated periodically to reflect changes made by political bodies 704616d0f9Sopenharmony_cito time zone boundaries and daylight saving rules. 714616d0f9Sopenharmony_ciThis database (known as <code><abbr>tz</abbr></code>, 724616d0f9Sopenharmony_ci<code><abbr>tzdb</abbr></code>, or <code>zoneinfo</code>) 734616d0f9Sopenharmony_ciis used by several implementations, 744616d0f9Sopenharmony_ciincluding 754616d0f9Sopenharmony_ci<a href="https://www.gnu.org/software/libc/">the 764616d0f9Sopenharmony_ci<abbr title="GNU's Not Unix">GNU</abbr> 774616d0f9Sopenharmony_ciC Library</a> (used in 784616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Linux"><abbr>GNU</abbr>/Linux</a>), 794616d0f9Sopenharmony_ci<a href="https://www.android.com">Android</a>, 804616d0f9Sopenharmony_ci<a href="https://www.freebsd.org">Free<abbr 814616d0f9Sopenharmony_cititle="Berkeley Software Distribution">BSD</abbr></a>, 824616d0f9Sopenharmony_ci<a href="https://netbsd.org">Net<abbr>BSD</abbr></a>, 834616d0f9Sopenharmony_ci<a href="https://www.openbsd.org">Open<abbr>BSD</abbr></a>, 844616d0f9Sopenharmony_ci<a href="https://www.chromium.org/chromium-os/">Chromium OS</a>, 854616d0f9Sopenharmony_ci<a href="https://cygwin.com">Cygwin</a>, 864616d0f9Sopenharmony_ci<a href="https://mariadb.org">MariaDB</a>, 874616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/MINIX">MINIX</a>, 884616d0f9Sopenharmony_ci<a href="https://www.mysql.com">MySQL</a>, 894616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/WebOS"><abbr 904616d0f9Sopenharmony_cititle="Web Operating System">webOS</abbr></a>, 914616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/IBM_AIX"><abbr 924616d0f9Sopenharmony_cititle="Advanced Interactive eXecutive">AIX</abbr></a>, 934616d0f9Sopenharmony_ci<a href="https://www.apple.com/ios"><abbr 944616d0f9Sopenharmony_cititle="iPhone OS">iOS</abbr></a>, 954616d0f9Sopenharmony_ci<a href="https://www.apple.com/macos">macOS</a>, 964616d0f9Sopenharmony_ci<a href="https://www.microsoft.com/en-us/windows">Microsoft Windows</a>, 974616d0f9Sopenharmony_ci<a href="https://www.vmssoftware.com">Open<abbr 984616d0f9Sopenharmony_cititle="Virtual Memory System">VMS</abbr></a>, 994616d0f9Sopenharmony_ci<a href="https://www.oracle.com/database/">Oracle Database</a>, and 1004616d0f9Sopenharmony_ci<a href="https://www.oracle.com/solaris">Oracle Solaris</a>.</p> 1014616d0f9Sopenharmony_ci<p> 1024616d0f9Sopenharmony_ciEach main entry in the database represents a <dfn>timezone</dfn> 1034616d0f9Sopenharmony_cifor a set of civil-time clocks that have all agreed since 1970. 1044616d0f9Sopenharmony_ciTimezones are typically identified by continent or ocean and then by the 1054616d0f9Sopenharmony_ciname of the largest city within the region containing the clocks. 1064616d0f9Sopenharmony_ciFor example, <code>America/New_York</code> 1074616d0f9Sopenharmony_cirepresents most of the <abbr title="United States">US</abbr> eastern time zone; 1084616d0f9Sopenharmony_ci<code>America/Phoenix</code> represents most of Arizona, which 1094616d0f9Sopenharmony_ciuses mountain time without daylight saving time (<abbr>DST</abbr>); 1104616d0f9Sopenharmony_ci<code>America/Detroit</code> represents most of Michigan, which uses 1114616d0f9Sopenharmony_cieastern time but with different <abbr>DST</abbr> rules in 1975; 1124616d0f9Sopenharmony_ciand other entries represent smaller regions like Starke County, 1134616d0f9Sopenharmony_ciIndiana, which switched from central to eastern time in 1991 1144616d0f9Sopenharmony_ciand switched back in 2006. 1154616d0f9Sopenharmony_ciTo use the database on an extended <a 1164616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/POSIX"><abbr 1174616d0f9Sopenharmony_cititle="Portable Operating System Interface">POSIX</abbr>.1-2017</a> 1184616d0f9Sopenharmony_ciimplementation set the <code><abbr>TZ</abbr></code> 1194616d0f9Sopenharmony_cienvironment variable to the location's full name, 1204616d0f9Sopenharmony_cie.g., <code><abbr>TZ</abbr>="America/New_York"</code>.</p> 1214616d0f9Sopenharmony_ci<p> 1224616d0f9Sopenharmony_ciAssociated with each timezone is a history of offsets from 1234616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Universal_Time">Universal 1244616d0f9Sopenharmony_ciTime</a> (<abbr>UT</abbr>), which is <a 1254616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Greenwich_Mean_Time">Greenwich Mean 1264616d0f9Sopenharmony_ciTime</a> (<abbr>GMT</abbr>) with days beginning at midnight; 1274616d0f9Sopenharmony_cifor timestamps after 1960 this is more precisely <a 1284616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">Coordinated 1294616d0f9Sopenharmony_ciUniversal Time</a> (<abbr>UTC</abbr>). 1304616d0f9Sopenharmony_ciThe database also records when daylight saving time was in use, 1314616d0f9Sopenharmony_cialong with some time zone abbreviations such as <abbr>EST</abbr> 1324616d0f9Sopenharmony_cifor Eastern Standard Time in the <abbr>US</abbr>.</p> 1334616d0f9Sopenharmony_ci</section> 1344616d0f9Sopenharmony_ci 1354616d0f9Sopenharmony_ci<section> 1364616d0f9Sopenharmony_ci<h2 id="download">Downloading the <code><abbr>tz</abbr></code> database</h2> 1374616d0f9Sopenharmony_ci<p> 1384616d0f9Sopenharmony_ciThe following <a 1394616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Unix_shell">shell</a> commands download 1404616d0f9Sopenharmony_cithe latest release's two 1414616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Tar_(computing)">tarballs</a> 1424616d0f9Sopenharmony_cito a <abbr>GNU</abbr>/Linux or similar host.</p> 1434616d0f9Sopenharmony_ci<pre><code>mkdir tzdb 1444616d0f9Sopenharmony_cicd tzdb 1454616d0f9Sopenharmony_ci<a href="https://www.gnu.org/software/wget/">wget</a> https://www.iana.org/time-zones/repository/tzcode-latest.tar.gz 1464616d0f9Sopenharmony_ciwget https://www.iana.org/time-zones/repository/tzdata-latest.tar.gz 1474616d0f9Sopenharmony_ci<a href="https://www.gnu.org/software/gzip/">gzip</a> -dc tzcode-latest.tar.gz | <a href="https://www.gnu.org/software/tar/">tar</a> -xf - 1484616d0f9Sopenharmony_cigzip -dc tzdata-latest.tar.gz | tar -xf - 1494616d0f9Sopenharmony_ci</code></pre> 1504616d0f9Sopenharmony_ci<p>Alternatively, the following shell commands download the same 1514616d0f9Sopenharmony_cirelease in a single-tarball format containing extra data 1524616d0f9Sopenharmony_ciuseful for regression testing:</p> 1534616d0f9Sopenharmony_ci<pre><code>wget <a href="https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz">https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz</a> 1544616d0f9Sopenharmony_ci<a href="https://www.nongnu.org/lzip/">lzip</a> -dc tzdb-latest.tar.lz | tar -xf - 1554616d0f9Sopenharmony_ci</code></pre> 1564616d0f9Sopenharmony_ci<p>These commands use convenience links to the latest release 1574616d0f9Sopenharmony_ciof the <code><abbr>tz</abbr></code> database hosted by the 1584616d0f9Sopenharmony_ci<a href="https://www.iana.org/time-zones">Time Zone Database website</a> 1594616d0f9Sopenharmony_ciof the <a href="https://www.iana.org">Internet Assigned Numbers 1604616d0f9Sopenharmony_ciAuthority (IANA)</a>. 1614616d0f9Sopenharmony_ciOlder releases are in files named 1624616d0f9Sopenharmony_ci<code>tzcode<var>V</var>.tar.gz</code>, 1634616d0f9Sopenharmony_ci<code>tzdata<var>V</var>.tar.gz</code>, and 1644616d0f9Sopenharmony_ci<code>tzdb-<var>V</var>.tar.lz</code>, 1654616d0f9Sopenharmony_ciwhere <code><var>V</var></code> is the version. 1664616d0f9Sopenharmony_ciSince 1996, each version has been a four-digit year followed by 1674616d0f9Sopenharmony_cilower-case letter (<samp>a</samp> through <samp>z</samp>, 1684616d0f9Sopenharmony_cithen <samp>za</samp> through <samp>zz</samp>, then <samp>zza</samp> 1694616d0f9Sopenharmony_cithrough <samp>zzz</samp>, and so on). 1704616d0f9Sopenharmony_ciSince version 2022a, each release has been distributed in 1714616d0f9Sopenharmony_ci<a href="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13_06">POSIX 1724616d0f9Sopenharmony_ciustar interchange format</a>, compressed as described above; 1734616d0f9Sopenharmony_ciolder releases use a nearly compatible format. 1744616d0f9Sopenharmony_ciSince version 2016h, each release has contained a text file named 1754616d0f9Sopenharmony_ci"<code>version</code>" whose first (and currently only) line is the version. 1764616d0f9Sopenharmony_ciOlder releases are <a href="https://ftp.iana.org/tz/releases/">archived</a>, 1774616d0f9Sopenharmony_ciand are also available in an 1784616d0f9Sopenharmony_ci<a href="ftp://ftp.iana.org/tz/releases/"><abbr 1794616d0f9Sopenharmony_cititle="File Transfer Protocol">FTP</abbr> directory</a> via a 1804616d0f9Sopenharmony_ciless secure protocol.</p> 1814616d0f9Sopenharmony_ci<p>Alternatively, a development repository of code and data can be 1824616d0f9Sopenharmony_ciretrieved from <a href="https://github.com">GitHub</a> via the shell 1834616d0f9Sopenharmony_cicommand:</p> 1844616d0f9Sopenharmony_ci<pre><code><a href="https://git-scm.com">git</a> clone <a href="https://github.com/eggert/tz">https://github.com/eggert/tz</a> 1854616d0f9Sopenharmony_ci</code></pre> 1864616d0f9Sopenharmony_ci<p> 1874616d0f9Sopenharmony_ciSince version 2012e, each release has been tagged in development repositories. 1884616d0f9Sopenharmony_ciUntagged commits are less well tested and probably contain 1894616d0f9Sopenharmony_cimore errors.</p> 1904616d0f9Sopenharmony_ci<p> 1914616d0f9Sopenharmony_ciAfter obtaining the code and data files, see the 1924616d0f9Sopenharmony_ci<code>README</code> file for what to do next. 1934616d0f9Sopenharmony_ciThe code lets you compile the <code><abbr>tz</abbr></code> source files into 1944616d0f9Sopenharmony_cimachine-readable binary files, one for each location. The binary files 1954616d0f9Sopenharmony_ciare in a special timezone information format (<dfn><abbr>TZif</abbr></dfn>) 1964616d0f9Sopenharmony_cispecified by <a href="https://datatracker.ietf.org/doc/html/8536">Internet 1974616d0f9Sopenharmony_ci<abbr>RFC</abbr> 8536</a>. 1984616d0f9Sopenharmony_ciThe code also lets 1994616d0f9Sopenharmony_ciyou read a <abbr>TZif</abbr> file and interpret timestamps for that 2004616d0f9Sopenharmony_cilocation.</p> 2014616d0f9Sopenharmony_ci</section> 2024616d0f9Sopenharmony_ci 2034616d0f9Sopenharmony_ci<section> 2044616d0f9Sopenharmony_ci<h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2> 2054616d0f9Sopenharmony_ci<p> 2064616d0f9Sopenharmony_ciThe <code><abbr>tz</abbr></code> code and data 2074616d0f9Sopenharmony_ciare by no means authoritative. If you find errors, please 2084616d0f9Sopenharmony_cisend changes to <a href="mailto:tz@iana.org"><code>tz@iana.org</code></a>, 2094616d0f9Sopenharmony_cithe time zone mailing list. You can also <a 2104616d0f9Sopenharmony_cihref="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it 2114616d0f9Sopenharmony_ciand browse the <a 2124616d0f9Sopenharmony_cihref="https://mm.icann.org/pipermail/tz/">archive of old 2134616d0f9Sopenharmony_cimessages</a>. 2144616d0f9Sopenharmony_ci<a href="https://tzdata-meta.timtimeonline.com/">Metadata for mailing list 2154616d0f9Sopenharmony_cidiscussions</a> and corresponding data changes can be 2164616d0f9Sopenharmony_cigenerated <a href="https://github.com/timparenti/tzdata-meta">automatically</a>. 2174616d0f9Sopenharmony_ci</p> 2184616d0f9Sopenharmony_ci<p> 2194616d0f9Sopenharmony_ciChanges to the <code><abbr>tz</abbr></code> code and data are often 2204616d0f9Sopenharmony_cipropagated to clients via operating system updates, so 2214616d0f9Sopenharmony_ciclient <code><abbr>tz</abbr></code> data can often be corrected by 2224616d0f9Sopenharmony_ciapplying these updates. With GNU/Linux and similar systems, if your 2234616d0f9Sopenharmony_cimaintenance provider has not yet adopted the 2244616d0f9Sopenharmony_cilatest <code><abbr>tz</abbr></code> data, you can often short-circuit 2254616d0f9Sopenharmony_cithe process by tailoring the generic instructions in 2264616d0f9Sopenharmony_cithe <code><abbr>tz</abbr> README</code> file and installing the latest 2274616d0f9Sopenharmony_cidata yourself. System-specific instructions for installing the 2284616d0f9Sopenharmony_cilatest <code><abbr>tz</abbr></code> data have also been published 2294616d0f9Sopenharmony_cifor <a href="https://developer.ibm.com/articles/au-aix-olson-time-zone/"><abbr>AIX</abbr></a>, 2304616d0f9Sopenharmony_ci<a 2314616d0f9Sopenharmony_cihref="https://source.android.com/devices/tech/config/timezone-rules">Android</a>, 2324616d0f9Sopenharmony_ci<a 2334616d0f9Sopenharmony_cihref="https://unicode-org.github.io/icu/userguide/datetime/timezone/"><abbr 2344616d0f9Sopenharmony_cititle="International Components for Unicode">ICU</abbr></a>, 2354616d0f9Sopenharmony_ci<a href="https://www.ibm.com/support/pages/java-sdk-time-zone-update-utility"><abbr>IBM</abbr> 2364616d0f9Sopenharmony_ciJDK</a>, 2374616d0f9Sopenharmony_ci<a href="https://www.joda.org/joda-time/tz_update.html">Joda-Time</a>, <a 2384616d0f9Sopenharmony_cihref="https://dev.mysql.com/doc/refman/en/time-zone-support.html">MySQL</a>, 2394616d0f9Sopenharmony_ci<a href="https://nodatime.org/userguide/tzdb">Noda Time</a>, and <a 2404616d0f9Sopenharmony_cihref="https://www.oracle.com/java/technologies/javase/tzupdater-readme.html">OpenJDK/Oracle JDK</a>. 2414616d0f9Sopenharmony_ci</p> 2424616d0f9Sopenharmony_ci<p>Since version 2013a, 2434616d0f9Sopenharmony_cisources for the <code><abbr>tz</abbr></code> database have been 2444616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/UTF-8"><abbr 2454616d0f9Sopenharmony_cititle="Unicode Transformation Format 8-bit">UTF-8</abbr></a> 2464616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Text_file">text files</a> 2474616d0f9Sopenharmony_ciwith lines terminated by <a href="https://en.wikipedia.org/wiki/Newline"><abbr 2484616d0f9Sopenharmony_cititle="linefeed">LF</abbr></a>, 2494616d0f9Sopenharmony_ciwhich can be modified by common text editors such 2504616d0f9Sopenharmony_cias <a href="https://www.gnu.org/software/emacs/">GNU Emacs</a>, 2514616d0f9Sopenharmony_ci<a href="https://wiki.gnome.org/Apps/Gedit">gedit</a>, and 2524616d0f9Sopenharmony_ci<a href="https://www.vim.org">vim</a>. 2534616d0f9Sopenharmony_ciSpecialized source-file editing can be done via the 2544616d0f9Sopenharmony_ci<a href="https://packagecontrol.io/packages/zoneinfo">Sublime 2554616d0f9Sopenharmony_cizoneinfo</a> package for <a 2564616d0f9Sopenharmony_cihref="https://www.sublimetext.com">Sublime Text</a> and the <a 2574616d0f9Sopenharmony_cihref="https://marketplace.visualstudio.com/items?itemName=gilmoreorless.vscode-zoneinfo">VSCode 2584616d0f9Sopenharmony_cizoneinfo</a> extension for <a href="https://code.visualstudio.com">Visual 2594616d0f9Sopenharmony_ciStudio Code</a>. 2604616d0f9Sopenharmony_ci</p> 2614616d0f9Sopenharmony_ci<p> 2624616d0f9Sopenharmony_ciFor further information about updates, please see 2634616d0f9Sopenharmony_ci<a href="https://datatracker.ietf.org/doc/html/rfc6557">Procedures for 2644616d0f9Sopenharmony_ciMaintaining the Time Zone Database</a> (Internet <abbr 2654616d0f9Sopenharmony_cititle="Request For Comments">RFC</abbr> 6557). More detail can be 2664616d0f9Sopenharmony_cifound in <a href="theory.html">Theory and pragmatics of the 2674616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> code and data</a>. 2684616d0f9Sopenharmony_ci<a href="https://a0.github.io/a0-tzmigration/">A0 TimeZone Migration</a> 2694616d0f9Sopenharmony_cidisplays changes between recent <code><abbr>tzdb</abbr></code> versions. 2704616d0f9Sopenharmony_ci</p> 2714616d0f9Sopenharmony_ci</section> 2724616d0f9Sopenharmony_ci 2734616d0f9Sopenharmony_ci<section> 2744616d0f9Sopenharmony_ci<h2 id="coordinating">Coordinating with governments and distributors</h2> 2754616d0f9Sopenharmony_ci<p> 2764616d0f9Sopenharmony_ciAs discussed in 2774616d0f9Sopenharmony_ci"<a href="https://www.icann.org/en/blogs/details/how-time-zones-are-coordinated-13-03-2023-en">How 2784616d0f9Sopenharmony_ciTime Zones Are Coordinated</a>", the time zone database relies on 2794616d0f9Sopenharmony_cicollaboration among governments, the time zone database volunteer 2804616d0f9Sopenharmony_cicommunity, and data distributors downstream. 2814616d0f9Sopenharmony_ci<p> 2824616d0f9Sopenharmony_ciIf your government plans to change its time zone boundaries or 2834616d0f9Sopenharmony_cidaylight saving rules, please send email to <a 2844616d0f9Sopenharmony_cihref="mailto:tz@iana.org"><code>tz@iana.org</code></a> well in advance, 2854616d0f9Sopenharmony_cias this will lessen confusion and will coordinate updates to many cell phones, 2864616d0f9Sopenharmony_cicomputers, and other devices around the world. 2874616d0f9Sopenharmony_ciIn your email, please cite the legislation or regulation that specifies 2884616d0f9Sopenharmony_cithe change, so that it can be checked for details such as the exact times 2894616d0f9Sopenharmony_ciwhen clock transitions occur. 2904616d0f9Sopenharmony_ciIt is OK if a rule change is planned to affect clocks 2914616d0f9Sopenharmony_cifar into the future, as a long-planned change can easily be reverted 2924616d0f9Sopenharmony_cior otherwise altered with a year's notice before the change would have 2934616d0f9Sopenharmony_ciaffected clocks.</p> 2944616d0f9Sopenharmony_ci<p> 2954616d0f9Sopenharmony_ciThere is no fixed schedule for <code><abbr>tzdb</abbr></code> releases. 2964616d0f9Sopenharmony_ciHowever, typically a release occurs every few months. 2974616d0f9Sopenharmony_ciMany downstream timezone data distributors wait for 2984616d0f9Sopenharmony_cia <code><abbr>tzdb</abbr></code> release before they produce an update 2994616d0f9Sopenharmony_cito time zone behavior in consumer devices and software products. 3004616d0f9Sopenharmony_ciAfter a release, various parties must integrate, test, 3014616d0f9Sopenharmony_ciand roll out an update before <a 3024616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/End_user">end users</a> see changes. 3034616d0f9Sopenharmony_ciThese updates can be expensive, for both the <a 3044616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Quality_assurance">quality 3054616d0f9Sopenharmony_ciassurance</a> process and the overall cost of shipping and installing 3064616d0f9Sopenharmony_ciupdates to each device's copy of <code><abbr>tzdb</abbr></code>. 3074616d0f9Sopenharmony_ciUpdates may be batched with other updates and may take substantial 3084616d0f9Sopenharmony_citime to reach end users after a release. 3094616d0f9Sopenharmony_ciOlder devices may no longer be supported and thus may never be updated, 3104616d0f9Sopenharmony_ciwhich means they will continue to use out-of-date rules.</p> 3114616d0f9Sopenharmony_ci<p> 3124616d0f9Sopenharmony_ciFor these reasons any rule change should be promulgated at least a 3134616d0f9Sopenharmony_ciyear before it affects how clocks operate; otherwise, there is a good 3144616d0f9Sopenharmony_cichance that many clocks will be wrong due to delays in propagating updates, 3154616d0f9Sopenharmony_ciand that residents will be confused or even actively resist the change. 3164616d0f9Sopenharmony_ciThe shorter the notice, the more likely clock problems will arise; see "<a 3174616d0f9Sopenharmony_cihref="https://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/">On 3184616d0f9Sopenharmony_cithe Timing of Time Zone Changes</a>" for examples. 3194616d0f9Sopenharmony_ci</p> 3204616d0f9Sopenharmony_ci</section> 3214616d0f9Sopenharmony_ci 3224616d0f9Sopenharmony_ci<section> 3234616d0f9Sopenharmony_ci<h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2> 3244616d0f9Sopenharmony_ci<ul> 3254616d0f9Sopenharmony_ci<li>The article 3264616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Tz_database">tz database</a> is 3274616d0f9Sopenharmony_cian encyclopedic summary.</li> 3284616d0f9Sopenharmony_ci<li><a href="tz-how-to.html">How to Read the 3294616d0f9Sopenharmony_citz Database Source Files</a> explains the <code><abbr>tz</abbr></code> 3304616d0f9Sopenharmony_cidatabase format.</li> 3314616d0f9Sopenharmony_ci<li><a 3324616d0f9Sopenharmony_cihref="https://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A 3334616d0f9Sopenharmony_ciliterary appreciation of the Olson/Zoneinfo/tz database</a> comments on the 3344616d0f9Sopenharmony_cidatabase's style.</li> 3354616d0f9Sopenharmony_ci<li><a href="https://doi.org/10.1145/3340301.3341125">What time is it: 3364616d0f9Sopenharmony_cimanaging time in the internet</a> analyzes the database longitudinally.</li> 3374616d0f9Sopenharmony_ci</ul> 3384616d0f9Sopenharmony_ci</section> 3394616d0f9Sopenharmony_ci 3404616d0f9Sopenharmony_ci<section> 3414616d0f9Sopenharmony_ci<h2 id="web">Web sites using recent versions of the 3424616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> database</h2> 3434616d0f9Sopenharmony_ci<p> 3444616d0f9Sopenharmony_ciThese are listed roughly in ascending order of complexity and fanciness. 3454616d0f9Sopenharmony_ci</p> 3464616d0f9Sopenharmony_ci<ul> 3474616d0f9Sopenharmony_ci<li><a href="https://time.is">Time.is</a> shows locations' 3484616d0f9Sopenharmony_citime and zones.</li> 3494616d0f9Sopenharmony_ci<li><a href="https://www.timejones.com">TimeJones.com</a>, 3504616d0f9Sopenharmony_ci<a href="https://timezoneconverterapp.com">Time Zone Converter</a> and 3514616d0f9Sopenharmony_ci<a href="https://www.worldclock.com">The World Clock</a> 3524616d0f9Sopenharmony_ciare time zone converters.</li> 3534616d0f9Sopenharmony_ci<li><a href="https://timezonedb.com/download">TimeZoneDB Database</a> 3544616d0f9Sopenharmony_cipublishes <code><abbr>tzdb</abbr></code>-derived data in 3554616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Comma-separated_values"><abbr 3564616d0f9Sopenharmony_cititle="comma-separated values">CSV</abbr></a> and 3574616d0f9Sopenharmony_ciin <a href="https://en.wikipedia.org/wiki/SQL"><abbr 3584616d0f9Sopenharmony_cititle="Structured Query Language">SQL</abbr></a> form.</li> 3594616d0f9Sopenharmony_ci<li><a 3604616d0f9Sopenharmony_cihref="https://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a> 3614616d0f9Sopenharmony_cilets you see the <code><abbr>TZ</abbr></code> values directly.</li> 3624616d0f9Sopenharmony_ci<li><a 3634616d0f9Sopenharmony_cihref="https://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current 3644616d0f9Sopenharmony_ciTime in 1000 Places</a> uses descriptions of the values.</li> 3654616d0f9Sopenharmony_ci<li><a href="https://www.timeanddate.com/worldclock/">The World Clock – 3664616d0f9Sopenharmony_ciWorldwide</a> lets you sort zone names and convert times.</li> 3674616d0f9Sopenharmony_ci<li><a href="https://24timezones.com">24TimeZones</a> has a world 3684616d0f9Sopenharmony_citime map and a time converter.</li> 3694616d0f9Sopenharmony_ci<li><a href="https://www.zeitverschiebung.net/en/">Time Difference</a> 3704616d0f9Sopenharmony_cicalculates the current time difference between locations.</li> 3714616d0f9Sopenharmony_ci<li><a href="https://www.wx-now.com">Weather Now</a> and 3724616d0f9Sopenharmony_ci<a href="https://www.thetimenow.com">The Time Now</a> list the weather too.</li> 3734616d0f9Sopenharmony_ci</ul> 3744616d0f9Sopenharmony_ci</section> 3754616d0f9Sopenharmony_ci 3764616d0f9Sopenharmony_ci<section> 3774616d0f9Sopenharmony_ci<h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2> 3784616d0f9Sopenharmony_ci<ul> 3794616d0f9Sopenharmony_ci<li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s 3804616d0f9Sopenharmony_ci<a href="https://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data 3814616d0f9Sopenharmony_ciDistribution Service (tzdist) working group</a> defined <a 3824616d0f9Sopenharmony_cihref="https://datatracker.ietf.org/doc/html/rfc7808">TZDIST</a> 3834616d0f9Sopenharmony_ci(Internet <abbr>RFC</abbr> 7808), a time zone data distribution service, 3844616d0f9Sopenharmony_cialong with <a href="https://datatracker.ietf.org/doc/html/rfc7809">CalDAV</a> 3854616d0f9Sopenharmony_ci(Internet <abbr>RFC</abbr> 7809), a calendar access protocol for 3864616d0f9Sopenharmony_citransferring time zone data by reference. 3874616d0f9Sopenharmony_ci<a href="https://devguide.calconnect.org/Time-Zones/TZDS/">TZDIST 3884616d0f9Sopenharmony_ciimplementations</a> are available. 3894616d0f9Sopenharmony_ciThe <a href="https://www.ietf.org/mailman/listinfo/tzdist-bis">tzdist-bis 3904616d0f9Sopenharmony_cimailing list</a> discusses possible extensions.</li> 3914616d0f9Sopenharmony_ci<li>The <a href="https://datatracker.ietf.org/doc/html/rfc5545"> 3924616d0f9Sopenharmony_ciInternet Calendaring and Scheduling Core Object Specification 3934616d0f9Sopenharmony_ci(iCalendar)</a> (Internet <abbr>RFC</abbr> 5445) 3944616d0f9Sopenharmony_cicovers time zone 3954616d0f9Sopenharmony_cidata; see its VTIMEZONE calendar component. 3964616d0f9Sopenharmony_ciThe iCalendar format requires specialized parsers and generators; a 3974616d0f9Sopenharmony_civariant <a href="https://datatracker.ietf.org/doc/html/rfc6321">xCal</a> 3984616d0f9Sopenharmony_ci(Internet <abbr>RFC</abbr> 6321) uses 3994616d0f9Sopenharmony_ci<a href="https://www.w3.org/XML/"><abbr 4004616d0f9Sopenharmony_cititle="Extensible Markup Language">XML</abbr></a> format, and a variant 4014616d0f9Sopenharmony_ci<a href="https://datatracker.ietf.org/doc/html/rfc7265">jCal</a> 4024616d0f9Sopenharmony_ci(Internet <abbr>RFC</abbr> 7265) 4034616d0f9Sopenharmony_ciuses <a href="https://www.json.org"><abbr 4044616d0f9Sopenharmony_cititle="JavaScript Object Notation">JSON</abbr></a> format.</li> 4054616d0f9Sopenharmony_ci</ul> 4064616d0f9Sopenharmony_ci</section> 4074616d0f9Sopenharmony_ci 4084616d0f9Sopenharmony_ci<section> 4094616d0f9Sopenharmony_ci<h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2> 4104616d0f9Sopenharmony_ci<p>Although some of these do not fully support 4114616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> data, in recent <code><abbr>tzdb</abbr></code> 4124616d0f9Sopenharmony_cidistributions you can generally work around compatibility problems by 4134616d0f9Sopenharmony_cirunning the command <code>make rearguard_tarballs</code> and compiling 4144616d0f9Sopenharmony_cifrom the resulting tarballs instead.</p> 4154616d0f9Sopenharmony_ci<ul> 4164616d0f9Sopenharmony_ci<li><a href="https://sourceforge.net/projects/vzic/">Vzic</a> is a <a 4174616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/C_(programming_language)">C</a> 4184616d0f9Sopenharmony_ciprogram that compiles 4194616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files. 4204616d0f9Sopenharmony_ciVzic is freely 4214616d0f9Sopenharmony_ciavailable under the <a 4224616d0f9Sopenharmony_cihref="https://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr> 4234616d0f9Sopenharmony_ciGeneral Public License (<abbr 4244616d0f9Sopenharmony_cititle="General Public License">GPL</abbr>)</a>.</li> 4254616d0f9Sopenharmony_ci<li><a href="https://sourceforge.net/projects/tzical/">tziCal – tz 4264616d0f9Sopenharmony_cidatabase conversion utility</a> is like Vzic, except for the <a 4274616d0f9Sopenharmony_cihref="https://dotnet.microsoft.com">.NET framework</a> 4284616d0f9Sopenharmony_ciand with a <abbr>BSD</abbr>-style license.</li> 4294616d0f9Sopenharmony_ci<li><a 4304616d0f9Sopenharmony_cihref="https://metacpan.org/release/DateTime-TimeZone">DateTime::TimeZone</a> 4314616d0f9Sopenharmony_cicontains a script <code>parse_olson</code> that compiles 4324616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> source into <a href="https://www.perl.org">Perl</a> 4334616d0f9Sopenharmony_cimodules. It is part of the Perl <a 4344616d0f9Sopenharmony_cihref="https://github.com/houseabsolute/DateTime.pm/wiki">DateTime Project</a>, 4354616d0f9Sopenharmony_ciwhich is freely 4364616d0f9Sopenharmony_ciavailable under both the <abbr>GPL</abbr> and the Perl Artistic 4374616d0f9Sopenharmony_ciLicense. DateTime::TimeZone also contains a script 4384616d0f9Sopenharmony_ci<code>tests_from_zdump</code> that generates test cases for each clock 4394616d0f9Sopenharmony_citransition in the <code><abbr>tz</abbr></code> database.</li> 4404616d0f9Sopenharmony_ci<li>The <a href="https://howardhinnant.github.io/date/tz.html">Time Zone 4414616d0f9Sopenharmony_ciDatabase Parser</a> is a 4424616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/C++">C++</a> parser and 4434616d0f9Sopenharmony_ciruntime library with <a 4444616d0f9Sopenharmony_cihref="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0355r7.html">API</a> 4454616d0f9Sopenharmony_ciadopted by 4464616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/C++20">C++20</a>, 4474616d0f9Sopenharmony_cithe current iteration of the C++ standard. 4484616d0f9Sopenharmony_ciIt is freely available under the 4494616d0f9Sopenharmony_ci<abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li> 4504616d0f9Sopenharmony_ci<li><a id="ICU" href="https://icu.unicode.org">International Components for 4514616d0f9Sopenharmony_ciUnicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a 4524616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Java_(programming_language)">Java</a> 4534616d0f9Sopenharmony_cilibraries for internationalization that 4544616d0f9Sopenharmony_cihas a compiler from <code><abbr>tz</abbr></code> source 4554616d0f9Sopenharmony_ciand from <abbr title="Common Locale Data Repository">CLDR</abbr> data 4564616d0f9Sopenharmony_ci(mentioned <a href="#CLDR">below</a>) 4574616d0f9Sopenharmony_ciinto an <abbr>ICU</abbr>-specific format. 4584616d0f9Sopenharmony_ci<abbr>ICU</abbr> is freely available under a 4594616d0f9Sopenharmony_ci<abbr>BSD</abbr>-style license.</li> 4604616d0f9Sopenharmony_ci<li>The <a href="https://github.com/lau/tzdata">Tzdata</a> package for 4614616d0f9Sopenharmony_cithe <a href="https://elixir-lang.org">Elixir</a> language downloads 4624616d0f9Sopenharmony_ciand compiles <code><abbr>tz</abbr></code> source and exposes <abbr 4634616d0f9Sopenharmony_cititle="Application Program Interface">API</abbr>s for use. It is 4644616d0f9Sopenharmony_cifreely available under the <abbr>MIT</abbr> license.</li> 4654616d0f9Sopenharmony_ci<li>Java-based compilers and libraries include: 4664616d0f9Sopenharmony_ci<ul> 4674616d0f9Sopenharmony_ci<li>The <a 4684616d0f9Sopenharmony_cihref="https://www.oracle.com/java/technologies/javase/tzupdater-readme.html">TZUpdater 4694616d0f9Sopenharmony_citool</a> compiles <code><abbr>tz</abbr></code> source into the format used by 4704616d0f9Sopenharmony_ci<a href="https://openjdk.java.net/">OpenJDK</a> and 4714616d0f9Sopenharmony_ci<a href="https://jdk.java.net/">Oracle JDK</a>. 4724616d0f9Sopenharmony_ciAlthough its source code is proprietary, its executable is available under the 4734616d0f9Sopenharmony_ci<a href="https://www.oracle.com/a/tech/docs/tzupdater-lic.html">Java SE 4744616d0f9Sopenharmony_ciTimezone Updater License Agreement</a>.</li> 4754616d0f9Sopenharmony_ci<li>The <a 4764616d0f9Sopenharmony_cihref="https://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html">Java 4774616d0f9Sopenharmony_ciSE 8 Date and Time</a> <abbr>API</abbr> can be supplemented by <a 4784616d0f9Sopenharmony_cihref="https://www.threeten.org/threeten-extra/">ThreeTen-Extra</a>, 4794616d0f9Sopenharmony_ciwhich is freely available under a <abbr>BSD</abbr>-style license.</li> 4804616d0f9Sopenharmony_ci<li><a href="https://www.joda.org/joda-time/">Joda-Time – Java date 4814616d0f9Sopenharmony_ciand time <abbr>API</abbr></a> contains a class 4824616d0f9Sopenharmony_ci<code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles 4834616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> source into a binary format. It inspired 4844616d0f9Sopenharmony_ciJava 8 <code>java.time</code>, which its users should migrate to once 4854616d0f9Sopenharmony_cithey can assume Java 8 or later. It is available under the <a 4864616d0f9Sopenharmony_cihref="https://www.apache.org/licenses/LICENSE-2.0">Apache License</a>.</li> 4874616d0f9Sopenharmony_ci<li><a href="https://bell-sw.com/pages/iana-updater/">IANA Updater</a> and <a 4884616d0f9Sopenharmony_cihref="https://www.azul.com/products/open-source-tools/ziupdater-time-zone-tool/">ZIUpdater</a> 4894616d0f9Sopenharmony_ciare alternatives to TZUpdater. IANA Updater's license is unclear; 4904616d0f9Sopenharmony_ciZIUpdater is licensed under the <abbr>GPL</abbr>.</li> 4914616d0f9Sopenharmony_ci<li><a href="https://github.com/MenoData/Time4A">Time4A: Advanced date and 4924616d0f9Sopenharmony_citime library for Android</a> and 4934616d0f9Sopenharmony_ci<a href="https://github.com/MenoData/Time4J/">Time4J: Advanced date, 4944616d0f9Sopenharmony_citime and interval library for Java</a> compile 4954616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> source into a binary format. 4964616d0f9Sopenharmony_ciTime4A is available under the Apache License and Time4J is 4974616d0f9Sopenharmony_ciavailable under the <a 4984616d0f9Sopenharmony_cihref="https://www.gnu.org/copyleft/lesser.html"><abbr>GNU</abbr> Lesser 4994616d0f9Sopenharmony_ciGeneral Public License (<abbr title="Lesser General Public 5004616d0f9Sopenharmony_ciLicense">LGPL</abbr>)</a>.</li> 5014616d0f9Sopenharmony_ci<li><abbr>ICU</abbr> (mentioned <a href="#ICU">above</a>) contains compilers and 5024616d0f9Sopenharmony_ciJava-based libraries.</li> 5034616d0f9Sopenharmony_ci</ul> 5044616d0f9Sopenharmony_ci<li><a href="https://nodatime.org">Noda Time – Date and 5054616d0f9Sopenharmony_citime <abbr>API</abbr> for .NET</a> 5064616d0f9Sopenharmony_ciis like Joda-Time and Time4J, but for the .NET framework instead of Java. 5074616d0f9Sopenharmony_ciIt is freely available under the Apache License.</li> 5084616d0f9Sopenharmony_ci<li>Many modern 5094616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/JavaScript">JavaScript</a> 5104616d0f9Sopenharmony_ciruntimes support <code><abbr>tz</abbr></code> natively via the 5114616d0f9Sopenharmony_ci<code>timeZone</code> option of <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat"><code>Intl.DateTimeFormat</code></a>. 5124616d0f9Sopenharmony_ciThis can be used as-is or with most of the following libraries, 5134616d0f9Sopenharmony_cimany of which also support runtimes lacking the <code>timeZone</code> option. 5144616d0f9Sopenharmony_ci<ul> 5154616d0f9Sopenharmony_ci<li>The <a 5164616d0f9Sopenharmony_cihref="https://github.com/formatjs/date-time-format-timezone"><code>Intl.DateTimeFormat</code> 5174616d0f9Sopenharmony_citimezone polyfill</a> 5184616d0f9Sopenharmony_ciis freely available under a <abbr>BSD</abbr>-style license.</li> 5194616d0f9Sopenharmony_ci<li>The <a href="https://date-fns.org/">date-fns</a> 5204616d0f9Sopenharmony_cilibrary manipulates timezone-aware timestamps in browsers and 5214616d0f9Sopenharmony_ciin <a href="https://nodejs.org/en/">Node.js</a>. 5224616d0f9Sopenharmony_ciIt is freely available under the <abbr>MIT</abbr> license.</li> 5234616d0f9Sopenharmony_ci<li><a href="https://github.com/iamkun/dayjs">Day.js</a> is a 5244616d0f9Sopenharmony_ciminimalist replacement for the date and time API of 5254616d0f9Sopenharmony_cithe <a href="https://momentjs.com/docs/">now-legacy Moment.js</a> date 5264616d0f9Sopenharmony_cimanipulation library. 5274616d0f9Sopenharmony_ciIt is freely available under the <abbr>MIT</abbr> license.</li> 5284616d0f9Sopenharmony_ci<li><a href="https://moment.github.io/luxon/">Luxon</a> improves 5294616d0f9Sopenharmony_citimezone support for the <code>Intl</code> API. 5304616d0f9Sopenharmony_ciIt is freely available under the <abbr>MIT</abbr> license.</li> 5314616d0f9Sopenharmony_ci<li><a href="https://momentjs.com/timezone/">Moment Timezone</a> is a 5324616d0f9Sopenharmony_ciMoment.js plugin. 5334616d0f9Sopenharmony_ciIt is freely available under the <abbr>MIT</abbr> license.</li> 5344616d0f9Sopenharmony_ci<li><a href="https://github.com/bigeasy/timezone">Timezone</a> is a 5354616d0f9Sopenharmony_ciJavaScript library that supports date arithmetic that is time zone 5364616d0f9Sopenharmony_ciaware. It is freely available under the <abbr>MIT</abbr> license.</li> 5374616d0f9Sopenharmony_ci<li><a href="https://www.npmjs.com/package/@tubular/time">@tubular/time</a> 5384616d0f9Sopenharmony_cisupports live <code><abbr>tzdb</abbr></code> updates, 5394616d0f9Sopenharmony_ciastronomical and atomic time, a command-line interface, 5404616d0f9Sopenharmony_ciand full <a 5414616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/TypeScript">TypeScript</a>. 5424616d0f9Sopenharmony_ciIts companion <a 5434616d0f9Sopenharmony_cihref="https://www.npmjs.com/package/@tubular/time-tzdb">@tubular/time-tzdb</a> 5444616d0f9Sopenharmony_cican generate <abbr>TZif</abbr> and other files, and a companion website 5454616d0f9Sopenharmony_ci<a href="https://tzexplorer.org">Timezone Database Explorer</a> lets you 5464616d0f9Sopenharmony_ciconvert timestamps, view transition histories, and download code and data. 5474616d0f9Sopenharmony_ciIt is freely available under the <abbr>MIT</abbr> license.</li> 5484616d0f9Sopenharmony_ci</ul> 5494616d0f9Sopenharmony_ciThe proposed <a 5504616d0f9Sopenharmony_cihref="https://github.com/tc39/proposal-temporal"><code>Temporal</code> 5514616d0f9Sopenharmony_ciobjects</a> let programs access an abstract view of 5524616d0f9Sopenharmony_ci<code><abbr>tzdb</abbr></code> data, and are designed to replace <a 5534616d0f9Sopenharmony_cihref="https://codeofmatt.com/javascript-date-type-is-horribly-broken/">JavaScript's 5544616d0f9Sopenharmony_ciproblematic <code>Date</code> objects</a> when working with dates and times. 5554616d0f9Sopenharmony_ci<li><a href="https://github.com/JuliaTime/">JuliaTime</a> contains a 5564616d0f9Sopenharmony_cicompiler from <code><abbr>tz</abbr></code> source into 5574616d0f9Sopenharmony_ci<a href="https://julialang.org/">Julia</a>. It is freely available 5584616d0f9Sopenharmony_ciunder the <abbr>MIT</abbr> license.</li> 5594616d0f9Sopenharmony_ci<li><a href="https://github.com/pavkam/tzdb"><abbr>TZDB</abbr> – 5604616d0f9Sopenharmony_ci<abbr>IANA</abbr> Time Zone Database for Delphi/<abbr 5614616d0f9Sopenharmony_cititle="Free Pascal Compiler">FPC</abbr></a> 5624616d0f9Sopenharmony_cicompiles from <code><abbr>tz</abbr></code> source into 5634616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Object_Pascal">Object Pascal</a> 5644616d0f9Sopenharmony_cias compiled by <a href="https://en.wikipedia.org/wiki/Delphi_(IDE)">Delphi</a> 5654616d0f9Sopenharmony_ciand <a 5664616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Free_Pascal"><abbr>FPC</abbr></a>. 5674616d0f9Sopenharmony_ciIt is freely available under a <abbr>BSD</abbr>-style license.</li> 5684616d0f9Sopenharmony_ci<li><a href="http://pytz.sourceforge.net">pytz – World Timezone 5694616d0f9Sopenharmony_ciDefinitions for Python</a> compiles <code><abbr>tz</abbr></code> source into 5704616d0f9Sopenharmony_ci<a href="https://www.python.org">Python</a>. 5714616d0f9Sopenharmony_ciIt is freely available under a <abbr>BSD</abbr>-style license. 5724616d0f9Sopenharmony_ciIn code that can assume Python 3.6 or later it is largely superseded; see <a 5734616d0f9Sopenharmony_cihref="https://blog.ganssle.io/articles/2018/03/pytz-fastest-footgun.html">pytz: 5744616d0f9Sopenharmony_ciThe Fastest Footgun in the West</a>.</li> 5754616d0f9Sopenharmony_ci<li><a href="https://tzinfo.github.io">TZInfo – 5764616d0f9Sopenharmony_ciRuby Timezone Library</a> 5774616d0f9Sopenharmony_cicompiles <code><abbr>tz</abbr></code> source into 5784616d0f9Sopenharmony_ci<a href="https://www.ruby-lang.org/en/">Ruby</a>. 5794616d0f9Sopenharmony_ciIt is freely available under the <abbr>MIT</abbr> license.</li> 5804616d0f9Sopenharmony_ci<li>The <a href="https://www.squeaksource.com/Chronos/">Chronos Date/Time 5814616d0f9Sopenharmony_ciLibrary</a> is 5824616d0f9Sopenharmony_cia <a href="https://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class 5834616d0f9Sopenharmony_cilibrary that compiles <code><abbr>tz</abbr></code> source into a time 5844616d0f9Sopenharmony_cizone repository whose format 5854616d0f9Sopenharmony_ciis either proprietary or an <abbr>XML</abbr>-encoded 5864616d0f9Sopenharmony_cirepresentation.</li> 5874616d0f9Sopenharmony_ci<li><a id="Tcl" href="https://tcl.tk">Tcl</a> 5884616d0f9Sopenharmony_cicontains a developer-oriented parser that compiles <code><abbr>tz</abbr></code> 5894616d0f9Sopenharmony_cisource into text files, along with a runtime that can read those 5904616d0f9Sopenharmony_cifiles. Tcl is freely available under a <abbr>BSD</abbr>-style 5914616d0f9Sopenharmony_cilicense.</li> 5924616d0f9Sopenharmony_ci</ul> 5934616d0f9Sopenharmony_ci</section> 5944616d0f9Sopenharmony_ci 5954616d0f9Sopenharmony_ci<section> 5964616d0f9Sopenharmony_ci<h2 id="TZif">Other <abbr>TZif</abbr> readers</h2> 5974616d0f9Sopenharmony_ci<ul> 5984616d0f9Sopenharmony_ci<li>The <a 5994616d0f9Sopenharmony_cihref="https://www.gnu.org/software/libc/"><abbr>GNU</abbr> C 6004616d0f9Sopenharmony_ciLibrary</a> 6014616d0f9Sopenharmony_cihas an independent, thread-safe implementation of 6024616d0f9Sopenharmony_cia <abbr>TZif</abbr> file reader. 6034616d0f9Sopenharmony_ciThis library is freely available under the LGPL 6044616d0f9Sopenharmony_ciand is widely used in <abbr>GNU</abbr>/Linux systems.</li> 6054616d0f9Sopenharmony_ci<li><a href="https://www.gnome.org">GNOME</a>'s 6064616d0f9Sopenharmony_ci<a href="https://developer.gnome.org/glib/">GLib</a> has 6074616d0f9Sopenharmony_cia <abbr>TZif</abbr> file reader written in C that 6084616d0f9Sopenharmony_cicreates a <code>GTimeZone</code> object representing sets 6094616d0f9Sopenharmony_ciof <abbr>UT</abbr> offsets. 6104616d0f9Sopenharmony_ciIt is freely available under the <abbr>LGPL</abbr>.</li> 6114616d0f9Sopenharmony_ci<li>The 6124616d0f9Sopenharmony_ci<a href="https://github.com/bloomberg/bde/wiki">BDE Standard Library</a>'s 6134616d0f9Sopenharmony_ci<code>baltzo::TimeZoneUtil</code> component contains a C++ 6144616d0f9Sopenharmony_ciimplementation of a <abbr>TZif</abbr> file reader. It is freely available under 6154616d0f9Sopenharmony_cithe Apache License.</li> 6164616d0f9Sopenharmony_ci<li><a href="https://github.com/google/cctz">CCTZ</a> is a simple C++ 6174616d0f9Sopenharmony_cilibrary that translates between <abbr>UT</abbr> and civil time and 6184616d0f9Sopenharmony_cican read <abbr>TZif</abbr> files. It is freely available under the Apache 6194616d0f9Sopenharmony_ciLicense.</li> 6204616d0f9Sopenharmony_ci<li>The 6214616d0f9Sopenharmony_ci<a href="https://github.com/nayarsystems/posix_tz_db"><code>posix_tz_db</code> 6224616d0f9Sopenharmony_cipackage</a> contains Python code 6234616d0f9Sopenharmony_cito generate <abbr>CSV</abbr> and <abbr>JSON</abbr> tables that map 6244616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> settings to POSIX.1-2017-like approximations. 6254616d0f9Sopenharmony_ciFor example, it maps <code>"Africa/Cairo"</code> 6264616d0f9Sopenharmony_cito <code>"EET-2EEST,M4.5.5/0,M10.5.4/24"</code>, 6274616d0f9Sopenharmony_cian approximation valid for Cairo timestamps from 2023 on. 6284616d0f9Sopenharmony_ciThis can help porting to platforms that support only POSIX.1-2017. 6294616d0f9Sopenharmony_ciThe package is freely available under the MIT license.</li> 6304616d0f9Sopenharmony_ci<li><a href="https://github.com/derickr/timelib">Timelib</a> is a C 6314616d0f9Sopenharmony_cilibrary that reads <abbr>TZif</abbr> files and converts 6324616d0f9Sopenharmony_citimestamps from one time zone or format to another. 6334616d0f9Sopenharmony_ciIt is used by <a href="https://secure.php.net"><abbr 6344616d0f9Sopenharmony_cititle="PHP: Hypertext Preprocessor">PHP</abbr></a>, 6354616d0f9Sopenharmony_ci<a href="https://hhvm.com"><abbr title="HipHop Virtual Machine">HHVM</abbr></a>, 6364616d0f9Sopenharmony_ciand <a href="https://www.mongodb.com">MongoDB</a>. 6374616d0f9Sopenharmony_ciIt is freely available under the <abbr>MIT</abbr> license.</li> 6384616d0f9Sopenharmony_ci<li>Tcl, mentioned <a href="#Tcl">above</a>, also contains a 6394616d0f9Sopenharmony_ci<abbr>TZif</abbr> file reader.</li> 6404616d0f9Sopenharmony_ci<li><a href="https://metacpan.org/pod/DateTime::TimeZone::Tzfile"> 6414616d0f9Sopenharmony_ciDateTime::TimeZone::Tzfile</a> 6424616d0f9Sopenharmony_ciis a <abbr>TZif</abbr> file reader written in Perl. 6434616d0f9Sopenharmony_ciIt is freely available under the same terms as Perl 6444616d0f9Sopenharmony_ci(dual <abbr>GPL</abbr> and Artistic license).</li> 6454616d0f9Sopenharmony_ci<li>Python has a <a id="python-zoneinfo" 6464616d0f9Sopenharmony_cihref="https://docs.python.org/3/library/zoneinfo.html"><code>zoneinfo.ZoneInfo</code> 6474616d0f9Sopenharmony_ciclass</a> that reads <abbr>TZif</abbr> data and creates objects 6484616d0f9Sopenharmony_cithat represent <code><abbr>tzdb</abbr></code> timezones. 6494616d0f9Sopenharmony_ciPython is freely available under the 6504616d0f9Sopenharmony_ci<a href="https://docs.python.org/3/license.html">Python Software Foundation 6514616d0f9Sopenharmony_ciLicense</a>. 6524616d0f9Sopenharmony_ciA companion <a id="pypi-tzdata" href="https://pypi.org/">PyPI</a> module 6534616d0f9Sopenharmony_ci<a href="https://pypi.org/project/tzdata/"><code>tzdata</code></a> 6544616d0f9Sopenharmony_cisupplies TZif data if the underlying system data cannot be found; 6554616d0f9Sopenharmony_ciit is freely available under the Apache License.</li> 6564616d0f9Sopenharmony_ci<li>The 6574616d0f9Sopenharmony_cipublic-domain <a href="https://github.com/dbaron/tz.js">tz.js</a> 6584616d0f9Sopenharmony_cilibrary contains a Python tool that 6594616d0f9Sopenharmony_ciconverts <abbr>TZif</abbr> data into 6604616d0f9Sopenharmony_ci<abbr>JSON</abbr>-format data suitable for use 6614616d0f9Sopenharmony_ciin its JavaScript library for time zone conversion. Dates before 1970 6624616d0f9Sopenharmony_ciare not supported.</li> 6634616d0f9Sopenharmony_ci<li>The <a 6644616d0f9Sopenharmony_cihref="https://hackage.haskell.org/package/timezone-olson">timezone-olson</a> 6654616d0f9Sopenharmony_cipackage contains <a href="https://www.haskell.org">Haskell</a> code that 6664616d0f9Sopenharmony_ciparses and uses <abbr>TZif</abbr> data. It is freely 6674616d0f9Sopenharmony_ciavailable under a <abbr>BSD</abbr>-style license.</li> 6684616d0f9Sopenharmony_ci</ul> 6694616d0f9Sopenharmony_ci</section> 6704616d0f9Sopenharmony_ci 6714616d0f9Sopenharmony_ci<section> 6724616d0f9Sopenharmony_ci<h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2> 6734616d0f9Sopenharmony_ci<ul> 6744616d0f9Sopenharmony_ci<li><a href="https://foxclocks.org">FoxClocks</a> 6754616d0f9Sopenharmony_ciis an extension for <a href="https://www.google.com/chrome/">Google 6764616d0f9Sopenharmony_ciChrome</a>, <a 6774616d0f9Sopenharmony_cihref="https://www.mozilla.org/en-US/firefox/new/">Firefox</a> and <a 6784616d0f9Sopenharmony_cihref="https://www.mozilla.org/en-US/thunderbird/">Thunderbird</a>. 6794616d0f9Sopenharmony_ciIt displays multiple clocks in the application window, and has a mapping 6804616d0f9Sopenharmony_ciinterface to <a href="https://www.google.com/earth/">Google Earth</a>. 6814616d0f9Sopenharmony_ciIt is freely available under the <abbr>GPL</abbr>.</li> 6824616d0f9Sopenharmony_ci<li><a href="https://golang.org">Go programming language</a> 6834616d0f9Sopenharmony_ciimplementations contain a copy of a 32-bit subset of a recent 6844616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> database in a 6854616d0f9Sopenharmony_ciGo-specific format.</li> 6864616d0f9Sopenharmony_ci<li>Microsoft Windows 8.1 6874616d0f9Sopenharmony_ciand later has <code><abbr>tz</abbr></code> data and <abbr>CLDR</abbr> 6884616d0f9Sopenharmony_cidata (mentioned <a href="#CLDR">below</a>) used by the 6894616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a> / 6904616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Universal_Windows_Platform">Universal Windows Platform</a> classes 6914616d0f9Sopenharmony_ci<a href="https://docs.microsoft.com/uwp/api/Windows.Globalization.DateTimeFormatting.DateTimeFormatter"><code>DateTimeFormatter</code></a> and 6924616d0f9Sopenharmony_ci<a href="https://docs.microsoft.com/uwp/api/windows.globalization.calendar"><code>Calendar</code></a>. 6934616d0f9Sopenharmony_ci<a id="System.TimeZoneInfo" 6944616d0f9Sopenharmony_cihref="https://blogs.msdn.microsoft.com/bclteam/2007/06/07/exploring-windows-time-zones-with-system-timezoneinfo-josh-free/">Exploring 6954616d0f9Sopenharmony_ciWindows Time Zones with <code>System.TimeZoneInfo</code></a> describes 6964616d0f9Sopenharmony_cithe older, proprietary method of Microsoft Windows 2000 and later, 6974616d0f9Sopenharmony_ciwhich stores time zone data in the 6984616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Windows_Registry">Windows Registry</a>. The 6994616d0f9Sopenharmony_ci<a 7004616d0f9Sopenharmony_cihref="https://unicode.org/cldr/charts/latest/supplemental/zone_tzid.html">Zone → 7014616d0f9Sopenharmony_ciTzid table</a> or <a 7024616d0f9Sopenharmony_cihref="https://github.com/unicode-org/cldr/blob/master/common/supplemental/windowsZones.xml"><abbr>XML</abbr> 7034616d0f9Sopenharmony_cifile</a> of the <abbr>CLDR</abbr> data maps proprietary zone IDs 7044616d0f9Sopenharmony_cito <code><abbr>tz</abbr></code> names. 7054616d0f9Sopenharmony_ciThese mappings can be performed programmatically via the <a href="https://github.com/mj1856/TimeZoneConverter">TimeZoneConverter</a> .NET library, 7064616d0f9Sopenharmony_cior the ICU Java and C++ libraries mentioned <a href="#ICU">above</a>. 7074616d0f9Sopenharmony_ci<li><a 7084616d0f9Sopenharmony_cihref="https://www.oracle.com/java/index.html">Oracle 7094616d0f9Sopenharmony_ciJava</a> contains a copy of a subset of a recent 7104616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> database in a 7114616d0f9Sopenharmony_ciJava-specific format.</li> 7124616d0f9Sopenharmony_ci</ul> 7134616d0f9Sopenharmony_ci</section> 7144616d0f9Sopenharmony_ci 7154616d0f9Sopenharmony_ci<section> 7164616d0f9Sopenharmony_ci<h2 id="other-dbs">Other time zone databases</h2> 7174616d0f9Sopenharmony_ci<ul> 7184616d0f9Sopenharmony_ci<li><a href="https://www.astro.com/atlas">Time-zone Atlas</a> 7194616d0f9Sopenharmony_ciis Astrodienst's Web version of Shanks and Pottenger's out-of-print 7204616d0f9Sopenharmony_citime zone history atlases 7214616d0f9Sopenharmony_ci<a href="https://www.worldcat.org/oclc/468828649">for the US</a> and 7224616d0f9Sopenharmony_ci<a href="https://www.worldcat.org/oclc/76950459">for the world</a>. 7234616d0f9Sopenharmony_ciAlthough these extensive atlases 7244616d0f9Sopenharmony_ci<a href="https://astrologynewsservice.com/opinion/how-astrologers-contributed-to-the-information-age-a-brief-history-of-time/">were 7254616d0f9Sopenharmony_cisources for much of the older <code><abbr>tz</abbr></code> data</a>, 7264616d0f9Sopenharmony_cithey are unreliable as Shanks appears to have 7274616d0f9Sopenharmony_ciguessed many <abbr>UT</abbr> offsets and transitions. The atlases cite no 7284616d0f9Sopenharmony_cisources and do not indicate which entries are guesswork.</li> 7294616d0f9Sopenharmony_ci<li><a href="https://en.wikipedia.org/wiki/HP-UX">HP-UX</a> has a database in 7304616d0f9Sopenharmony_ciits own <code>tztab</code>(4) format.</li> 7314616d0f9Sopenharmony_ci<li>Microsoft Windows has proprietary data mentioned 7324616d0f9Sopenharmony_ci<a href="#System.TimeZoneInfo">above</a>.</li> 7334616d0f9Sopenharmony_ci<li><a href="https://www.worldtimeserver.com">World Time Server</a> 7344616d0f9Sopenharmony_ciis another time zone database.</li> 7354616d0f9Sopenharmony_ci<li>The <a 7364616d0f9Sopenharmony_cihref="https://www.iata.org/publications/store/Pages/standard-schedules-information.aspx">Standard 7374616d0f9Sopenharmony_ciSchedules Information Manual</a> of the 7384616d0f9Sopenharmony_ciInternational Air Transport Association 7394616d0f9Sopenharmony_cigives current time zone rules for airports served by commercial aviation.</li> 7404616d0f9Sopenharmony_ci</ul> 7414616d0f9Sopenharmony_ci</section> 7424616d0f9Sopenharmony_ci 7434616d0f9Sopenharmony_ci<section> 7444616d0f9Sopenharmony_ci<h2 id="maps">Maps</h2> 7454616d0f9Sopenharmony_ci<ul> 7464616d0f9Sopenharmony_ci<li>The <a 7474616d0f9Sopenharmony_cihref="https://www.cia.gov/the-world-factbook/maps/world-regional/">World 7484616d0f9Sopenharmony_ciand Regional Maps section</a> of <em>The World Factbook</em>, published by the 7494616d0f9Sopenharmony_ci<a href="https://www.cia.gov">US Central Intelligence 7504616d0f9Sopenharmony_ciAgency (<abbr 7514616d0f9Sopenharmony_cititle="Central Intelligence Agency">CIA</abbr>)</a>, contains a time 7524616d0f9Sopenharmony_cizone map; the 7534616d0f9Sopenharmony_ci<a 7544616d0f9Sopenharmony_cihref="https://legacy.lib.utexas.edu/maps/world.html">Perry–Castañeda 7554616d0f9Sopenharmony_ciLibrary Map Collection</a> 7564616d0f9Sopenharmony_ciof the University of Texas at Austin has copies of 7574616d0f9Sopenharmony_cirecent editions. 7584616d0f9Sopenharmony_ciThe pictorial quality is good, 7594616d0f9Sopenharmony_cibut the maps do not indicate daylight saving time, 7604616d0f9Sopenharmony_ciand parts of the data are a few years out of date.</li> 7614616d0f9Sopenharmony_ci<li><a href="https://www.worldtimezone.com">World Time Zone Map 7624616d0f9Sopenharmony_ciwith current time</a> 7634616d0f9Sopenharmony_cihas several fancy time zone maps; it covers Russia particularly well. 7644616d0f9Sopenharmony_ciThe maps' pictorial quality is not quite as good as the 7654616d0f9Sopenharmony_ci<abbr>CIA</abbr>'s 7664616d0f9Sopenharmony_cibut the maps are more up to date.</li> 7674616d0f9Sopenharmony_ci<li><a 7684616d0f9Sopenharmony_cihref="https://blog.poormansmath.net/how-much-is-time-wrong-around-the-world/">How 7694616d0f9Sopenharmony_cimuch is time wrong around the world?</a> maps the difference between 7704616d0f9Sopenharmony_cimean solar and standard time, highlighting areas such as western China 7714616d0f9Sopenharmony_ciwhere the two differ greatly. It's a bit out of date, unfortunately.</li> 7724616d0f9Sopenharmony_ci</ul> 7734616d0f9Sopenharmony_ci</section> 7744616d0f9Sopenharmony_ci 7754616d0f9Sopenharmony_ci<section> 7764616d0f9Sopenharmony_ci<h2 id="boundaries">Time zone boundaries</h2> 7774616d0f9Sopenharmony_ci<p>Geographical boundaries between timezones are available 7784616d0f9Sopenharmony_cifrom several <a 7794616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Internet_geolocation">Internet 7804616d0f9Sopenharmony_cigeolocation</a> 7814616d0f9Sopenharmony_ciservices and other sources.</p> 7824616d0f9Sopenharmony_ci<ul> 7834616d0f9Sopenharmony_ci<li><a href="https://github.com/evansiroky/timezone-boundary-builder">Timezone 7844616d0f9Sopenharmony_ciBoundary Builder</a> extracts 7854616d0f9Sopenharmony_ci<a href="https://www.openstreetmap.org">Open Street Map</a> data to build 7864616d0f9Sopenharmony_ciboundaries of <code><abbr>tzdb</abbr></code> timezones. 7874616d0f9Sopenharmony_ciIts code is freely available under the <abbr>MIT</abbr> license, and 7884616d0f9Sopenharmony_ciits data entries are freely available under the 7894616d0f9Sopenharmony_ci<a href="https://opendatacommons.org/licenses/odbl/">Open Data Commons 7904616d0f9Sopenharmony_ciOpen Database License</a>. The borders appear to be quite accurate. 7914616d0f9Sopenharmony_ciIts main web page lists more than twenty libraries 7924616d0f9Sopenharmony_cifor looking up a timezone name from a GPS coordinate.</li> 7934616d0f9Sopenharmony_ci<li>Free access via a network API, if you register a key, is provided by 7944616d0f9Sopenharmony_cithe <a 7954616d0f9Sopenharmony_cihref="https://www.geonames.org/export/web-services.html#timezone">GeoNames 7964616d0f9Sopenharmony_ciTimezone web service</a>, the <a 7974616d0f9Sopenharmony_cihref="https://developers.google.com/maps/documentation/timezone/intro">Google 7984616d0f9Sopenharmony_ciMaps Time Zone API</a>, and 7994616d0f9Sopenharmony_cithe <a href="https://timezonedb.com/api">TimeZoneDB API</a>. 8004616d0f9Sopenharmony_ciCommercial network API access is provided 8014616d0f9Sopenharmony_ciby <a href="https://askgeo.com">AskGeo</a> 8024616d0f9Sopenharmony_ciand <a href="https://www.geogarage.com/blog/news-1/post/geogarage-time-zone-api-31">GeoGarage</a>. 8034616d0f9Sopenharmony_ci</li> 8044616d0f9Sopenharmony_ci<li>"<a 8054616d0f9Sopenharmony_cihref="https://stackoverflow.com/questions/16086962/how-to-get-a-time-zone-from-a-location-using-latitude-and-longitude-coordinates/16086964">How 8064616d0f9Sopenharmony_cito get a time zone from a location using latitude and longitude 8074616d0f9Sopenharmony_cicoordinates?</a>" discusses other geolocation possibilities.</li> 8084616d0f9Sopenharmony_ci<li><a href="http://statoids.com/statoids.html">Administrative 8094616d0f9Sopenharmony_ciDivisions of Countries ("Statoids")</a> lists 8104616d0f9Sopenharmony_cipolitical subdivision data related to time zones.</li> 8114616d0f9Sopenharmony_ci<li><a href="https://manifold.net/info/freestuff.shtml">Manifold Software 8124616d0f9Sopenharmony_ci– GIS and Database Tools</a> includes a Manifold-format map of 8134616d0f9Sopenharmony_ciworld time zone boundaries circa 2007, distributed under the 8144616d0f9Sopenharmony_ci<abbr>GPL</abbr>.</li> 8154616d0f9Sopenharmony_ci<li>A ship within the <a 8164616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Territorial_waters">territorial 8174616d0f9Sopenharmony_ciwaters</a> of any nation uses that nation's time. In international 8184616d0f9Sopenharmony_ciwaters, time zone boundaries are meridians 15° apart, except that 8194616d0f9Sopenharmony_ci<abbr>UT</abbr>−12 and <abbr>UT</abbr>+12 are each 7.5° 8204616d0f9Sopenharmony_ciwide and are separated by 8214616d0f9Sopenharmony_cithe 180° meridian (not by the International Date Line, which is 8224616d0f9Sopenharmony_cifor land and territorial waters only). A captain can change ship's 8234616d0f9Sopenharmony_ciclocks any time after entering a new time zone; midnight changes are 8244616d0f9Sopenharmony_cicommon.</li> 8254616d0f9Sopenharmony_ci</ul> 8264616d0f9Sopenharmony_ci</section> 8274616d0f9Sopenharmony_ci 8284616d0f9Sopenharmony_ci<section> 8294616d0f9Sopenharmony_ci<h2 id="civil">Civil time concepts and history</h2> 8304616d0f9Sopenharmony_ci<ul> 8314616d0f9Sopenharmony_ci<li><a href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-through-time">A 8324616d0f9Sopenharmony_ciWalk through Time</a> 8334616d0f9Sopenharmony_cisurveys the evolution of timekeeping.</li> 8344616d0f9Sopenharmony_ci<li>The history of daylight saving time is surveyed in <a 8354616d0f9Sopenharmony_cihref="http://www.webexhibits.org/daylightsaving/">About Daylight 8364616d0f9Sopenharmony_ciSaving Time – History, rationale, laws & dates</a> and summarized in 8374616d0f9Sopenharmony_ci<a href="http://seizethedaylight.com/dst/">A Brief 8384616d0f9Sopenharmony_ciHistory of Daylight Saving Time</a>.</li> 8394616d0f9Sopenharmony_ci<li><a href="https://www.laphamsquarterly.org/roundtable/time-lords">Time 8404616d0f9Sopenharmony_ciLords</a> discusses how authoritarians manipulate civil time.</li> 8414616d0f9Sopenharmony_ci<li><a href="https://www.w3.org/TR/timezone/">Working with Time Zones</a> 8424616d0f9Sopenharmony_cicontains guidelines and best practices for software applications that 8434616d0f9Sopenharmony_cideal with civil time.</li> 8444616d0f9Sopenharmony_ci<li><a href="https://webspace.science.uu.nl/~gent0113/idl/idl.htm">A History of 8454616d0f9Sopenharmony_cithe International Date Line</a> tells the story of the most important 8464616d0f9Sopenharmony_citime zone boundary.</li> 8474616d0f9Sopenharmony_ci<li><a href="http://statoids.com/tconcept.html">Basic Time 8484616d0f9Sopenharmony_ciZone Concepts</a> discusses terminological issues behind time zones.</li> 8494616d0f9Sopenharmony_ci</ul> 8504616d0f9Sopenharmony_ci</section> 8514616d0f9Sopenharmony_ci 8524616d0f9Sopenharmony_ci<section> 8534616d0f9Sopenharmony_ci<h2 id="national">National histories of legal time</h2> 8544616d0f9Sopenharmony_ci<dl> 8554616d0f9Sopenharmony_ci<dt>Australia</dt> 8564616d0f9Sopenharmony_ci<dd>The Parliamentary Library commissioned a <a 8574616d0f9Sopenharmony_cihref="https://parlinfo.aph.gov.au/parlInfo/download/library/prspub/359V6/upload_binary/359v60.pdf">research 8584616d0f9Sopenharmony_cipaper on daylight saving time in Australia</a>. 8594616d0f9Sopenharmony_ciThe Bureau of Meteorology publishes a list of <a 8604616d0f9Sopenharmony_cihref="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation 8614616d0f9Sopenharmony_ciDates of Daylight Savings Time within Australia</a>.</dd> 8624616d0f9Sopenharmony_ci<dt>Belgium</dt> 8634616d0f9Sopenharmony_ci<dd>The Royal Observatory of Belgium maintains a table of time in 8644616d0f9Sopenharmony_ciBelgium (in 8654616d0f9Sopenharmony_ci<a href="https://robinfo.oma.be/nl/astro-info/tijd/" 8664616d0f9Sopenharmony_cihreflang="nl">Dutch</a> and <a 8674616d0f9Sopenharmony_cihref="https://robinfo.oma.be/fr/astro-info/heure/" 8684616d0f9Sopenharmony_cihreflang="fr">French</a>).</dd> 8694616d0f9Sopenharmony_ci<dt>Brazil</dt> 8704616d0f9Sopenharmony_ci<dd>The Time Service Department of the National Observatory 8714616d0f9Sopenharmony_cirecords <a href="http://pcdsh01.on.br/DecHV.html" 8724616d0f9Sopenharmony_cihreflang="pt-BR">Brazil's daylight saving time decrees (in 8734616d0f9Sopenharmony_ciPortuguese)</a>.</dd> 8744616d0f9Sopenharmony_ci<dt>Canada</dt> 8754616d0f9Sopenharmony_ci<dd>National Research Council Canada publishes current 8764616d0f9Sopenharmony_ciand some older information about <a 8774616d0f9Sopenharmony_cihref="https://nrc.canada.ca/en/certifications-evaluations-standards/canadas-official-time/time-zones-daylight-saving-time">time 8784616d0f9Sopenharmony_cizones and daylight saving time</a>.</dd> 8794616d0f9Sopenharmony_ci<dt>Chile</dt> 8804616d0f9Sopenharmony_ci<dd>The Hydrographic and Oceanographic Service of the Chilean Navy publishes a 8814616d0f9Sopenharmony_ci<a href="https://www.horaoficial.cl/historia_hora.php" hreflang="es">history of 8824616d0f9Sopenharmony_ciChile's official time (in Spanish)</a>.</dd> 8834616d0f9Sopenharmony_ci<dt>China</dt> 8844616d0f9Sopenharmony_ci<dd>The Hong Kong Observatory maintains a 8854616d0f9Sopenharmony_ci<a href="https://www.hko.gov.hk/en/gts/time/Summertime.htm">history of 8864616d0f9Sopenharmony_ci summer time in Hong Kong</a>, 8874616d0f9Sopenharmony_ciand Macau's Meteorological and Geophysical Bureau maintains a <a 8884616d0f9Sopenharmony_cihref="https://www.smg.gov.mo/en/subpage/224/page/174">similar 8894616d0f9Sopenharmony_cihistory for Macau</a>. 8904616d0f9Sopenharmony_ciUnfortunately the latter is incomplete and has errors.</dd> 8914616d0f9Sopenharmony_ci<dt>Czech Republic</dt> 8924616d0f9Sopenharmony_ci<dd><a href="https://kalendar.beda.cz/kdy-zacina-a-konci-letni-cas" 8934616d0f9Sopenharmony_cihreflang="cs">When daylight saving time starts and ends (in Czech)</a> 8944616d0f9Sopenharmony_cisummarizes and cites historical <abbr>DST</abbr> regulations.</dd> 8954616d0f9Sopenharmony_ci<dt>Germany</dt> 8964616d0f9Sopenharmony_ci<dd>The National Institute for Science and Technology maintains the <a 8974616d0f9Sopenharmony_cihref="https://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany.html">Realisation 8984616d0f9Sopenharmony_ciof Legal Time in Germany</a>.</dd> 8994616d0f9Sopenharmony_ci<dt>Israel</dt> 9004616d0f9Sopenharmony_ci<dd>The Interior Ministry periodically issues <a 9014616d0f9Sopenharmony_cihref="ftp://ftp.cs.huji.ac.il/pub/tz/announcements" 9024616d0f9Sopenharmony_cihreflang="he">announcements (in Hebrew)</a>.</dd> 9034616d0f9Sopenharmony_ci<dt>Malaysia</dt> 9044616d0f9Sopenharmony_ci<dd>See Singapore <a href="#Singapore">below</a>.</dd> 9054616d0f9Sopenharmony_ci<dt>Mexico</dt> 9064616d0f9Sopenharmony_ci<dd>The Investigation and Analysis Service of the Mexican Library of 9074616d0f9Sopenharmony_ciCongress has published a <a 9084616d0f9Sopenharmony_cihref="https://www.diputados.gob.mx/bibliot/publica/inveyana/polisoc/horver/index.htm" 9094616d0f9Sopenharmony_cihreflang="es">history of Mexican local time (in Spanish)</a>.</dd> 9104616d0f9Sopenharmony_ci<dt>Netherlands</dt> 9114616d0f9Sopenharmony_ci<dd><a href="https://webspace.science.uu.nl/~gent0113/wettijd/wettijd.htm" 9124616d0f9Sopenharmony_cihreflang="nl">Legal time in the Netherlands (in Dutch)</a> 9134616d0f9Sopenharmony_cicovers the history of local time in the Netherlands from ancient times.</dd> 9144616d0f9Sopenharmony_ci<dt>New Zealand</dt> 9154616d0f9Sopenharmony_ci<dd>The Department of Internal Affairs maintains a brief <a 9164616d0f9Sopenharmony_cihref="https://www.dia.govt.nz/Daylight-Saving-History">History of 9174616d0f9Sopenharmony_ciDaylight Saving</a>.</dd> 9184616d0f9Sopenharmony_ci<dt>Palestine</dt> 9194616d0f9Sopenharmony_ci<dd>The Ministry of Telecom and IT publishes a <a 9204616d0f9Sopenharmony_cihref="https://mtit.pna.ps/home/TimeZone" 9214616d0f9Sopenharmony_cihreflang="ar">history of clock changes (in Arabic)</a>.</dd> 9224616d0f9Sopenharmony_ci<dt>Portugal</dt> 9234616d0f9Sopenharmony_ci<dd>The Lisbon Astronomical Observatory publishes a 9244616d0f9Sopenharmony_ci<a href="https://oal.ul.pt/hora-legal/" hreflang="pt">history of 9254616d0f9Sopenharmony_cilegal time (in Portuguese)</a>.</dd> 9264616d0f9Sopenharmony_ci<dt>Singapore</dt> 9274616d0f9Sopenharmony_ci<dd><a id="Singapore" 9284616d0f9Sopenharmony_cihref="https://web.archive.org/web/20190822231045/http://www.math.nus.edu.sg/~mathelmr/teaching/timezone.html">Why 9294616d0f9Sopenharmony_ciis Singapore in the "Wrong" Time Zone?</a> details the 9304616d0f9Sopenharmony_cihistory of legal time in Singapore and Malaysia.</dd> 9314616d0f9Sopenharmony_ci<dt>United Kingdom</dt> 9324616d0f9Sopenharmony_ci<dd><a 9334616d0f9Sopenharmony_cihref="https://www.polyomino.org.uk/british-time/">History of 9344616d0f9Sopenharmony_cilegal time in Britain</a> discusses in detail the country 9354616d0f9Sopenharmony_ciwith perhaps the best-documented history of clock adjustments.</dd> 9364616d0f9Sopenharmony_ci<dt>United States</dt> 9374616d0f9Sopenharmony_ci<dd>The Department of Transportation's <a 9384616d0f9Sopenharmony_cihref="https://www.transportation.gov/regulations/recent-time-zone-proceedings">Recent 9394616d0f9Sopenharmony_ciTime Zone Proceedings</a> lists changes to time zone boundaries.</dd> 9404616d0f9Sopenharmony_ci<dt>Uruguay</dt> 9414616d0f9Sopenharmony_ci<dd>The Oceanography, Hydrography, and Meteorology Service of the Uruguayan 9424616d0f9Sopenharmony_ciNavy (SOHMA) publishes an annual <a 9434616d0f9Sopenharmony_cihref="https://sohma.armada.mil.uy/index.php/servicios/datos-astronomicos" hreflang="es">almanac 9444616d0f9Sopenharmony_ci(in Spanish)</a>.</dd> 9454616d0f9Sopenharmony_ci</dl> 9464616d0f9Sopenharmony_ci</section> 9474616d0f9Sopenharmony_ci 9484616d0f9Sopenharmony_ci<section> 9494616d0f9Sopenharmony_ci<h2 id="costs">Costs and benefits of time shifts</h2> 9504616d0f9Sopenharmony_ci<p>Various sources argue for and against daylight saving time and time 9514616d0f9Sopenharmony_cizone shifts, and many scientific studies have been conducted. This 9524616d0f9Sopenharmony_cisection summarizes reviews and position statements based on 9534616d0f9Sopenharmony_ciscientific literature in the area.</p> 9544616d0f9Sopenharmony_ci<ul> 9554616d0f9Sopenharmony_ci<li>In 2022 the American Medical Association issued a 9564616d0f9Sopenharmony_ci<a href="https://www.ama-assn.org/press-center/press-releases/ama-calls-permanent-standard-time">statement 9574616d0f9Sopenharmony_cisupporting permanent standard time</a> on health grounds.</li> 9584616d0f9Sopenharmony_ci<li>Carey RN, Sarma KM. 9594616d0f9Sopenharmony_ci<a href="https://bmjopen.bmj.com/content/7/6/e014319.long">Impact of 9604616d0f9Sopenharmony_cidaylight saving time on road traffic collision risk: a systematic 9614616d0f9Sopenharmony_cireview</a>. 9624616d0f9Sopenharmony_ci<em>BMJ Open.</em> 2017;7(6):e014319. doi:<a href="https://doi.org/10.1136/bmjopen-2016-014319">10.1136/bmjopen-2016-014319</a>. 9634616d0f9Sopenharmony_ciThis reviews research literature and concludes that the evidence 9644616d0f9Sopenharmony_cineither supports nor refutes road safety benefits from 9654616d0f9Sopenharmony_cishifts in time zones.</li> 9664616d0f9Sopenharmony_ci<li>Havranek T, Herman D, Irsova D. 9674616d0f9Sopenharmony_ci<a href="https://www.iaee.org/en/publications/ejarticle.aspx?id=3051">Does 9684616d0f9Sopenharmony_cidaylight saving save electricity? A meta-analysis</a>. 9694616d0f9Sopenharmony_ci<em>Energy J.</em> 2018;39(2):35–61. 9704616d0f9Sopenharmony_cidoi:<a href="https://doi.org/10.5547/01956574.39.2.thav">10.5547/01956574.39.2.thav</a>. 9714616d0f9Sopenharmony_ciThis analyzes research literature and concludes, "Electricity savings 9724616d0f9Sopenharmony_ciare larger for countries farther away from the equator, while 9734616d0f9Sopenharmony_cisubtropical regions consume more electricity because of <abbr>DST</abbr>."</li> 9744616d0f9Sopenharmony_ci<li>Malow BA. <a 9754616d0f9Sopenharmony_cihref="https://academic.oup.com/sleep/article/45/12/zsac236/6717940">It is time 9764616d0f9Sopenharmony_cito abolish the clock change and adopt permanent 9774616d0f9Sopenharmony_cistandard time in the United States: 9784616d0f9Sopenharmony_cia Sleep Research Society position statement</a>. 9794616d0f9Sopenharmony_ci<em>Sleep.</em> 2022;45(12):zsac236. 9804616d0f9Sopenharmony_cidoi:<a href="https://doi.org/10.1093/sleep/zsac236">10.1093/sleep/zsac236</a>. 9814616d0f9Sopenharmony_ciAfter reviewing the scientific literature, the Sleep Research Society 9824616d0f9Sopenharmony_ciadvocates permanent standard time due to its health benefits. 9834616d0f9Sopenharmony_ci<li>Rishi MA, Cheng JY, Strang AR <em>et al</em>. 9844616d0f9Sopenharmony_ci<a href="https://jcsm.aasm.org/doi/10.5664/jcsm.10898">Permanent standard time 9854616d0f9Sopenharmony_ciis the optimal choice for health and safety: 9864616d0f9Sopenharmony_cian American Academy of Sleep Medicine position statement</a>. 9874616d0f9Sopenharmony_ci<em>J Clin Sleep Med.</em> 2024;20(1):121–125. 9884616d0f9Sopenharmony_cidoi:<a href="https://doi.org/10.5664/jcsm.10898">10.5664/jcsm.10898</a>. 9894616d0f9Sopenharmony_ciThe AASM argues for permanent standard time due to health and safety risks 9904616d0f9Sopenharmony_ciand economic costs of both <abbr>DST</abbr> transitions and 9914616d0f9Sopenharmony_cipermanent <abbr>DST</abbr>.</li> 9924616d0f9Sopenharmony_ci<li>Roenneberg T, Wirz-Justice A, Skene DJ <em>et al</em>. 9934616d0f9Sopenharmony_ci<a href="https://journals.sagepub.com/doi/10.1177/0748730419854197">Why 9944616d0f9Sopenharmony_cishould we abolish Daylight Saving Time?</a> 9954616d0f9Sopenharmony_ci<em>J Biol Rhythms.</em> 2019;34(3):227–230. 9964616d0f9Sopenharmony_cidoi:<a href="https://doi.org/10.1177/0748730419854197">10.1177/0748730419854197</a>. 9974616d0f9Sopenharmony_ciThe Society for Research on Biological Rhythms 9984616d0f9Sopenharmony_ciopposes DST changes and permanent DST, and advocates that governments adopt 9994616d0f9Sopenharmony_ci"permanent Standard Time for the health and safety of their citizens".</li> 10004616d0f9Sopenharmony_ci</ul> 10014616d0f9Sopenharmony_ci</section> 10024616d0f9Sopenharmony_ci 10034616d0f9Sopenharmony_ci<section> 10044616d0f9Sopenharmony_ci<h2 id="precision">Precision timekeeping</h2> 10054616d0f9Sopenharmony_ci<ul> 10064616d0f9Sopenharmony_ci<li><a 10074616d0f9Sopenharmony_cihref="http://leapsecond.com/hpan/an1289.pdf">The 10084616d0f9Sopenharmony_ciScience of Timekeeping</a> is a thorough introduction 10094616d0f9Sopenharmony_cito the theory and practice of precision timekeeping.</li> 10104616d0f9Sopenharmony_ci<li><a href="https://doi.org/10.1007/978-3-319-59909-0">The Science of 10114616d0f9Sopenharmony_ciTime 2016</a> contains several freely readable papers.</li> 10124616d0f9Sopenharmony_ci<li><a href="https://www.ntp.org"><abbr 10134616d0f9Sopenharmony_cititle="Network Time Protocol">NTP</abbr>: The Network 10144616d0f9Sopenharmony_ciTime Protocol</a> (Internet <abbr>RFC</abbr> 5905) 10154616d0f9Sopenharmony_cidiscusses how to synchronize clocks of 10164616d0f9Sopenharmony_ciInternet hosts.</li> 10174616d0f9Sopenharmony_ci<li>The <a href="https://www.usenix.org/system/files/conference/nsdi18/nsdi18-geng.pdf"><span style="font-variant: small-caps">Huygens</span></a> 10184616d0f9Sopenharmony_cifamily of software algorithms can achieve accuracy to a few tens of 10194616d0f9Sopenharmony_cinanoseconds in scalable server farms without special hardware.</li> 10204616d0f9Sopenharmony_ci<li>The <a 10214616d0f9Sopenharmony_cihref="https://www.nist.gov/intelligent-systems-division/ieee-1588">Precision 10224616d0f9Sopenharmony_ciTime Protocol</a> (<abbr 10234616d0f9Sopenharmony_cititle="Institute of Electrical and Electronics Engineers">IEEE</abbr> 1588) 10244616d0f9Sopenharmony_cican achieve submicrosecond clock accuracy on a local area network 10254616d0f9Sopenharmony_ciwith special-purpose hardware.</li> 10264616d0f9Sopenharmony_ci<li><a 10274616d0f9Sopenharmony_cihref="https://datatracker.ietf.org/doc/html/rfc4833">Timezone 10284616d0f9Sopenharmony_ciOptions for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a> 10294616d0f9Sopenharmony_ci(Internet <abbr>RFC</abbr> 4833) 10304616d0f9Sopenharmony_cispecifies a <a 10314616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol"><abbr>DHCP</abbr></a> 10324616d0f9Sopenharmony_cioption for a server to configure 10334616d0f9Sopenharmony_cia client's time zone and daylight saving settings automatically.</li> 10344616d0f9Sopenharmony_ci<li><a href="https://www.ucolick.org/~sla/leapsecs/timescales.html">Time 10354616d0f9Sopenharmony_ciScales</a> describes astronomical time scales like 10364616d0f9Sopenharmony_ci<abbr title="Terrestrial Dynamic Time">TDT</abbr>, 10374616d0f9Sopenharmony_ci<abbr title="Geocentric Coordinate Time">TCG</abbr>, and 10384616d0f9Sopenharmony_ci<abbr title="Barycentric Dynamic Time">TDB</abbr>. 10394616d0f9Sopenharmony_ci<li>The <a href="https://www.iau.org"><abbr 10404616d0f9Sopenharmony_cititle="International Astronomical Union">IAU</abbr></a>'s <a 10414616d0f9Sopenharmony_cihref="https://www.iausofa.org"><abbr 10424616d0f9Sopenharmony_cititle="Standards Of Fundamental Astronomy">SOFA</abbr></a> 10434616d0f9Sopenharmony_cicollection contains C and <a 10444616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Fortran">Fortran</a> 10454616d0f9Sopenharmony_cicode for converting among time scales like 10464616d0f9Sopenharmony_ci<abbr title="International Atomic Time">TAI</abbr>, 10474616d0f9Sopenharmony_ci<abbr>TDB</abbr>, <abbr>TDT</abbr> and 10484616d0f9Sopenharmony_ci<abbr>UTC</abbr>. It is freely available under the 10494616d0f9Sopenharmony_ci<a href="https://www.iausofa.org/tandc.html">SOFA license</a>.</li> 10504616d0f9Sopenharmony_ci<li><a 10514616d0f9Sopenharmony_cihref="https://www.giss.nasa.gov/tools/mars24/help/notes.html">Mars24 Sunclock 10524616d0f9Sopenharmony_ci– Time on Mars</a> describes Airy Mean Time (<abbr>AMT</abbr>) and the 10534616d0f9Sopenharmony_cidiverse local time 10544616d0f9Sopenharmony_ciscales used by each landed mission on Mars.</li> 10554616d0f9Sopenharmony_ci<li><a href="http://leapsecond.com">LeapSecond.com</a> is 10564616d0f9Sopenharmony_cidedicated not only to leap seconds but to precise time and frequency 10574616d0f9Sopenharmony_ciin general. It covers the state of the art in amateur timekeeping, and 10584616d0f9Sopenharmony_cihow the art has progressed over the past few decades.</li> 10594616d0f9Sopenharmony_ci<li>The rules for leap seconds are specified in Annex 1 (Time scales) of <a 10604616d0f9Sopenharmony_cihref="https://www.itu.int/rec/R-REC-TF.460-6-200202-I/">Standard-frequency 10614616d0f9Sopenharmony_ciand time-signal emissions</a>, International Telecommunication Union – 10624616d0f9Sopenharmony_ciRadiocommunication Sector (ITU-R) Recommendation TF.460-6 (02/2002).</li> 10634616d0f9Sopenharmony_ci<li><a 10644616d0f9Sopenharmony_cihref="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr 10654616d0f9Sopenharmony_cititle="International Earth Rotation and Reference Systems Service">IERS</abbr> 10664616d0f9Sopenharmony_ciBulletins</a> contains official publications of the International 10674616d0f9Sopenharmony_ciEarth Rotation and Reference Systems Service, which decides when leap 10684616d0f9Sopenharmony_ciseconds occur. The <code><abbr>tz</abbr></code> code and data support leap seconds 10694616d0f9Sopenharmony_civia an optional "<code>right</code>" configuration where a computer's internal 10704616d0f9Sopenharmony_ci<code>time_t</code> integer clock counts every <abbr>TAI</abbr> second, 10714616d0f9Sopenharmony_cias opposed to the default "<code>posix</code>" configuration 10724616d0f9Sopenharmony_ciwhere the internal clock ignores leap seconds. 10734616d0f9Sopenharmony_ciThe two configurations agree for timestamps starting with 1972-01-01 00:00:00 10744616d0f9Sopenharmony_ci<abbr>UTC</abbr> (<code>time_t</code> 63 072 000) and diverge for 10754616d0f9Sopenharmony_citimestamps starting with <code>time_t</code> 78 796 800, 10764616d0f9Sopenharmony_ciwhich corresponds to the first leap second 10774616d0f9Sopenharmony_ci1972-06-30 23:59:60 <abbr>UTC</abbr> in the "<code>right</code>" configuration, 10784616d0f9Sopenharmony_ciand to 10794616d0f9Sopenharmony_ci1972-07-01 00:00:00 <abbr>UTC</abbr> in the "<code>posix</code>" configuration. 10804616d0f9Sopenharmony_ciIn practice the two configurations also agree for timestamps before 10814616d0f9Sopenharmony_ci1972 even though the historical situation is messy, partly because 10824616d0f9Sopenharmony_cineither <abbr>UTC</abbr> nor <abbr>TAI</abbr> 10834616d0f9Sopenharmony_ciis well-defined for sufficiently old timestamps.</li> 10844616d0f9Sopenharmony_ci<li><a href="https://developers.google.com/time/smear">Leap Smear</a> 10854616d0f9Sopenharmony_cidiscusses how to gradually adjust <abbr>POSIX</abbr> clocks near a 10864616d0f9Sopenharmony_cileap second so that they disagree with <abbr>UTC</abbr> by at most a 10874616d0f9Sopenharmony_cihalf second, even though every <abbr>POSIX</abbr> minute has exactly 10884616d0f9Sopenharmony_cisixty seconds. This approach works with the default <code><abbr>tz</abbr></code> 10894616d0f9Sopenharmony_ci"<code>posix</code>" configuration, is <a 10904616d0f9Sopenharmony_cihref="http://bk1.ntp.org/ntp-stable/README.leapsmear">supported</a> by 10914616d0f9Sopenharmony_cithe <abbr>NTP</abbr> reference implementation, <a 10924616d0f9Sopenharmony_cihref="https://github.com/google/unsmear">supports</a> conversion between 10934616d0f9Sopenharmony_ci<abbr>UTC</abbr> and smeared <abbr>POSIX</abbr> timestamps, and is used by major 10944616d0f9Sopenharmony_cicloud service providers. However, according to 10954616d0f9Sopenharmony_ci<a href="https://datatracker.ietf.org/doc/html/rfc8633#section-3.7.1">§3.7.1 of 10964616d0f9Sopenharmony_ciNetwork Time Protocol Best Current Practices</a> 10974616d0f9Sopenharmony_ci(Internet <abbr>RFC</abbr> 8633), leap smearing is not suitable for 10984616d0f9Sopenharmony_ciapplications requiring accurate <abbr>UTC</abbr> or civil time, 10994616d0f9Sopenharmony_ciand is intended for use only in single, well-controlled environments.</li> 11004616d0f9Sopenharmony_ci<li>The <a 11014616d0f9Sopenharmony_cihref="https://pairlist6.pair.net/mailman/listinfo/leapsecs">Leap 11024616d0f9Sopenharmony_ciSecond Discussion List</a> covers <a 11034616d0f9Sopenharmony_cihref="https://www2.unb.ca/gge/Resources/gpsworld.november99.pdf">McCarthy 11044616d0f9Sopenharmony_ciand Klepczynski's 1999 proposal to discontinue leap seconds</a>, 11054616d0f9Sopenharmony_cidiscussed further in 11064616d0f9Sopenharmony_ci<a href="https://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The 11074616d0f9Sopenharmony_cileap second: its history and possible future</a>. 11084616d0f9Sopenharmony_ci<a href="https://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr> 11094616d0f9Sopenharmony_cimight be redefined 11104616d0f9Sopenharmony_ciwithout Leap Seconds</a> gives pointers on this 11114616d0f9Sopenharmony_cicontentious issue. 11124616d0f9Sopenharmony_ciThe General Conference on Weights and Measures 11134616d0f9Sopenharmony_ci<a href="https://www.bipm.org/en/cgpm-2022/resolution-4">decided in 2022</a> 11144616d0f9Sopenharmony_cito discontinue the use of leap seconds by 2035, replacing them with an 11154616d0f9Sopenharmony_cias-yet-undetermined scheme some time after the year 2135. 11164616d0f9Sopenharmony_ciThe World Radiocommunication Conference <a 11174616d0f9Sopenharmony_cihref="https://www.itu.int/dms_pub/itu-r/opb/act/R-ACT-WRC.15-2023-PDF-E.pdf">resolved 11184616d0f9Sopenharmony_ciin 2023</a> to cooperate with this process. 11194616d0f9Sopenharmony_ci</li> 11204616d0f9Sopenharmony_ci</ul> 11214616d0f9Sopenharmony_ci</section> 11224616d0f9Sopenharmony_ci 11234616d0f9Sopenharmony_ci<section> 11244616d0f9Sopenharmony_ci<h2 id="notation">Time notation</h2> 11254616d0f9Sopenharmony_ci<ul> 11264616d0f9Sopenharmony_ci<li>The <a id="CLDR" href="https://cldr.unicode.org">Unicode Common Locale Data 11274616d0f9Sopenharmony_ciRepository (<abbr>CLDR</abbr>) Project</a> has localizations for time 11284616d0f9Sopenharmony_cizone names, abbreviations, identifiers, and formats. For example, it 11294616d0f9Sopenharmony_cicontains French translations for "Eastern European Summer Time", 11304616d0f9Sopenharmony_ci"<abbr title="Eastern European Summer Time">EEST</abbr>", and 11314616d0f9Sopenharmony_ci"Bucharest". Its 11324616d0f9Sopenharmony_ci<a href="https://unicode.org/cldr/charts/latest/by_type/">by-type 11334616d0f9Sopenharmony_cicharts</a> show these values for many locales. Data values are available in 11344616d0f9Sopenharmony_ciboth <abbr title="Locale Data Markup Language">LDML</abbr> 11354616d0f9Sopenharmony_ci(an <abbr>XML</abbr> format) and <abbr>JSON</abbr>. 11364616d0f9Sopenharmony_ci<li> 11374616d0f9Sopenharmony_ci<a href="https://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of 11384616d0f9Sopenharmony_cithe international standard date and time notation</a> covers 11394616d0f9Sopenharmony_ci<a 11404616d0f9Sopenharmony_cihref="https://www.iso.org/standard/70907.html"><em><abbr 11414616d0f9Sopenharmony_cititle="International Organization for Standardization">ISO</abbr> 11424616d0f9Sopenharmony_ci8601-1:2019 – Date and time – Representations for information 11434616d0f9Sopenharmony_ciinterchange – Part 1: Basic rules</em></a>.</li> 11444616d0f9Sopenharmony_ci<li> 11454616d0f9Sopenharmony_ci<a href="https://www.w3.org/TR/xmlschema/#dateTime"><abbr>XML</abbr> 11464616d0f9Sopenharmony_ciSchema: Datatypes – dateTime</a> specifies a format inspired by 11474616d0f9Sopenharmony_ci<abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li> 11484616d0f9Sopenharmony_ci<li><a href="https://datatracker.ietf.org/doc/html/rfc5322#section-3.3">§3.3 of 11494616d0f9Sopenharmony_ciInternet Message Format</a> (Internet <abbr>RFC</abbr> 5322) 11504616d0f9Sopenharmony_cispecifies the time notation used in email and <a 11514616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol"><abbr>HTTP</abbr></a> 11524616d0f9Sopenharmony_ciheaders.</li> 11534616d0f9Sopenharmony_ci<li> 11544616d0f9Sopenharmony_ci<a href="https://datatracker.ietf.org/doc/html/rfc3339">Date and Time 11554616d0f9Sopenharmony_cion the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339) 11564616d0f9Sopenharmony_cispecifies an <abbr>ISO</abbr> 8601 11574616d0f9Sopenharmony_ciprofile for use in new Internet 11584616d0f9Sopenharmony_ciprotocols.</li> 11594616d0f9Sopenharmony_ci<li> 11604616d0f9Sopenharmony_ci<a href="https://web.archive.org/web/20190130042457/https://www.hackcraft.net/web/datetime/">Date & Time 11614616d0f9Sopenharmony_ciFormats on the Web</a> surveys web- and Internet-oriented date and time 11624616d0f9Sopenharmony_ciformats.</li> 11634616d0f9Sopenharmony_ci<li>Alphabetic time zone abbreviations should not be used as unique 11644616d0f9Sopenharmony_ciidentifiers for <abbr>UT</abbr> offsets as they are ambiguous in 11654616d0f9Sopenharmony_cipractice. For example, in English-speaking North America 11664616d0f9Sopenharmony_ci"<abbr>CST</abbr>" denotes 6 hours behind <abbr>UT</abbr>, 11674616d0f9Sopenharmony_cibut in China it denotes 8 hours ahead of <abbr>UT</abbr>, 11684616d0f9Sopenharmony_ciand French-speaking North Americans prefer 11694616d0f9Sopenharmony_ci"<abbr title="Heure Normale du Centre">HNC</abbr>" to 11704616d0f9Sopenharmony_ci"<abbr>CST</abbr>". The <code><abbr>tz</abbr></code> 11714616d0f9Sopenharmony_cidatabase contains English abbreviations for many timestamps; 11724616d0f9Sopenharmony_ciunfortunately some of these abbreviations were merely the database maintainers' 11734616d0f9Sopenharmony_ciinventions, and these have been removed when possible.</li> 11744616d0f9Sopenharmony_ci<li>Numeric time zone abbreviations typically count hours east of 11754616d0f9Sopenharmony_ci<abbr>UT</abbr>, e.g., +09 for Japan and 11764616d0f9Sopenharmony_ci−10 for Hawaii. However, the <abbr>POSIX</abbr> 11774616d0f9Sopenharmony_ci<code><abbr>TZ</abbr></code> environment variable uses the opposite convention. 11784616d0f9Sopenharmony_ciFor example, one might use <code><abbr>TZ</abbr>="<abbr 11794616d0f9Sopenharmony_cititle="Japan Standard Time">JST</abbr>-9"</code> and 11804616d0f9Sopenharmony_ci<code><abbr>TZ</abbr>="<abbr title="Hawaii Standard Time">HST</abbr>10"</code> 11814616d0f9Sopenharmony_cifor Japan and Hawaii, respectively. If the 11824616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> database is available, it is usually better to use 11834616d0f9Sopenharmony_cisettings like <code><abbr>TZ</abbr>="Asia/Tokyo"</code> and 11844616d0f9Sopenharmony_ci<code><abbr>TZ</abbr>="Pacific/Honolulu"</code> instead, as this should avoid 11854616d0f9Sopenharmony_ciconfusion, handle old timestamps better, and insulate you better from 11864616d0f9Sopenharmony_ciany future changes to the rules. One should never set 11874616d0f9Sopenharmony_ci<abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> to a value like 11884616d0f9Sopenharmony_ci<code>"GMT-9"</code>, though, since this would incorrectly imply that 11894616d0f9Sopenharmony_cilocal time is nine hours ahead of <abbr>UT</abbr> and the time zone 11904616d0f9Sopenharmony_ciis called "<abbr>GMT</abbr>".</li> 11914616d0f9Sopenharmony_ci</ul> 11924616d0f9Sopenharmony_ci</section> 11934616d0f9Sopenharmony_ci 11944616d0f9Sopenharmony_ci<section> 11954616d0f9Sopenharmony_ci<h2 id="see-also">See also</h2> 11964616d0f9Sopenharmony_ci<ul> 11974616d0f9Sopenharmony_ci<li><a href="theory.html">Theory and pragmatics of the 11984616d0f9Sopenharmony_ci<code><abbr>tz</abbr></code> code and data</a></li> 11994616d0f9Sopenharmony_ci<li><a href="tz-art.html">Time and the Arts</a></li> 12004616d0f9Sopenharmony_ci</ul> 12014616d0f9Sopenharmony_ci</section> 12024616d0f9Sopenharmony_ci 12034616d0f9Sopenharmony_ci<footer> 12044616d0f9Sopenharmony_ci<hr> 12054616d0f9Sopenharmony_ciThis web page is in the public domain, so clarified as of 12064616d0f9Sopenharmony_ci2009-05-17 by Arthur David Olson. 12074616d0f9Sopenharmony_ci<br> 12084616d0f9Sopenharmony_ciPlease send corrections to this web page to the 12094616d0f9Sopenharmony_ci<a href="mailto:tz@iana.org">time zone mailing list</a>. 12104616d0f9Sopenharmony_ci</footer> 12114616d0f9Sopenharmony_ci</body> 12124616d0f9Sopenharmony_ci</html> 1213