14616d0f9Sopenharmony_ci<!DOCTYPE html> 24616d0f9Sopenharmony_ci<html lang="en"> 34616d0f9Sopenharmony_ci<head> 44616d0f9Sopenharmony_ci<title>How to Read the tz Database</title> 54616d0f9Sopenharmony_ci<meta charset="UTF-8"> 64616d0f9Sopenharmony_ci<style> 74616d0f9Sopenharmony_cipre {margin-left: 2em; white-space: pre-wrap;} 84616d0f9Sopenharmony_cipre.td {margin-left: 0;} 94616d0f9Sopenharmony_citd {text-align: center;} 104616d0f9Sopenharmony_citable {border: 1px outset;} 114616d0f9Sopenharmony_cith, td {border: 1px inset;} 124616d0f9Sopenharmony_citable.rule {border: none; margin: auto;} 134616d0f9Sopenharmony_citd.footnote {text-align: left;} 144616d0f9Sopenharmony_ci</style> 154616d0f9Sopenharmony_ci</head> 164616d0f9Sopenharmony_ci<body> 174616d0f9Sopenharmony_ci<h2>How to Read the <a href="https://en.wikipedia.org/wiki/Tz_database">tz 184616d0f9Sopenharmony_ciDatabase</a> Source Files</h2> 194616d0f9Sopenharmony_ci<h3>by Bill Seymour</h3> 204616d0f9Sopenharmony_ci<p>This guide uses the <code>America/Chicago</code> and 214616d0f9Sopenharmony_ci<code>Pacific/Honolulu</code> zones as examples of how to infer 224616d0f9Sopenharmony_citimes of day from the <a href="tz-link.html">tz database</a> 234616d0f9Sopenharmony_cisource files. It might be helpful, but not absolutely necessary, 244616d0f9Sopenharmony_cifor the reader to have already downloaded the 254616d0f9Sopenharmony_cilatest release of the database and become familiar with the basic layout 264616d0f9Sopenharmony_ciof the data files. The format is explained in the “man 274616d0f9Sopenharmony_cipage” for the zic compiler, <code>zic.8.txt</code>, in 284616d0f9Sopenharmony_cithe <code>code</code> subdirectory. 294616d0f9Sopenharmony_ciAlthough this guide covers many of the common cases, it is not a 304616d0f9Sopenharmony_cicomplete summary of what zic accepts; the man page is the 314616d0f9Sopenharmony_ciauthoritative reference.</p> 324616d0f9Sopenharmony_ci 334616d0f9Sopenharmony_ci<p>We’ll begin by talking about the rules for changing between standard 344616d0f9Sopenharmony_ciand daylight saving time since we’ll need that information when we talk 354616d0f9Sopenharmony_ciabout the zones.</p> 364616d0f9Sopenharmony_ci 374616d0f9Sopenharmony_ci<p>First, let’s consider the special daylight saving time rules 384616d0f9Sopenharmony_cifor Chicago (from the <code>northamerica</code> file in 394616d0f9Sopenharmony_cithe <code>data</code> subdirectory):</p> 404616d0f9Sopenharmony_ci 414616d0f9Sopenharmony_ci<table> 424616d0f9Sopenharmony_ci<tr> 434616d0f9Sopenharmony_ci <th colspan="6">From the Source File</th> 444616d0f9Sopenharmony_ci</tr> 454616d0f9Sopenharmony_ci<tr> 464616d0f9Sopenharmony_ci <td colspan="6"> 474616d0f9Sopenharmony_ci <table class="rule"> 484616d0f9Sopenharmony_ci <tr><td style="border:none;text-align:left"> 494616d0f9Sopenharmony_ci<pre class="td"> 504616d0f9Sopenharmony_ci#Rule NAME FROM TO - IN ON AT SAVE LETTER 514616d0f9Sopenharmony_ciRule Chicago 1920 only - Jun 13 2:00 1:00 D 524616d0f9Sopenharmony_ciRule Chicago 1920 1921 - Oct lastSun 2:00 0 S 534616d0f9Sopenharmony_ciRule Chicago 1921 only - Mar lastSun 2:00 1:00 D 544616d0f9Sopenharmony_ciRule Chicago 1922 1966 - Apr lastSun 2:00 1:00 D 554616d0f9Sopenharmony_ciRule Chicago 1922 1954 - Sep lastSun 2:00 0 S 564616d0f9Sopenharmony_ciRule Chicago 1955 1966 - Oct lastSun 2:00 0 S 574616d0f9Sopenharmony_ci</pre> 584616d0f9Sopenharmony_ci </td></tr></table></td> 594616d0f9Sopenharmony_ci</tr> 604616d0f9Sopenharmony_ci<tr> 614616d0f9Sopenharmony_ci <th colspan="6">Reformatted a Bit</th> 624616d0f9Sopenharmony_ci</tr> 634616d0f9Sopenharmony_ci<tr> 644616d0f9Sopenharmony_ci <th>From</th> 654616d0f9Sopenharmony_ci <th>To</th> 664616d0f9Sopenharmony_ci <th colspan="2">On</th> 674616d0f9Sopenharmony_ci <th>At</th> 684616d0f9Sopenharmony_ci <th>Action</th> 694616d0f9Sopenharmony_ci</tr> 704616d0f9Sopenharmony_ci<tr> 714616d0f9Sopenharmony_ci <td colspan="2">1920 only</td> 724616d0f9Sopenharmony_ci <td colspan="2">June 13<small><sup>th</sup></small></td> 734616d0f9Sopenharmony_ci <td rowspan="6">02:00 local</td> 744616d0f9Sopenharmony_ci <td>go to daylight saving time</td> 754616d0f9Sopenharmony_ci</tr> 764616d0f9Sopenharmony_ci<tr> 774616d0f9Sopenharmony_ci <td>1920</td> 784616d0f9Sopenharmony_ci <td>1921</td> 794616d0f9Sopenharmony_ci <td rowspan="5">last Sunday</td> 804616d0f9Sopenharmony_ci <td>in October</td> 814616d0f9Sopenharmony_ci <td>return to standard time</td> 824616d0f9Sopenharmony_ci</tr> 834616d0f9Sopenharmony_ci<tr> 844616d0f9Sopenharmony_ci <td colspan="2">1921 only</td> 854616d0f9Sopenharmony_ci <td>in March</td> 864616d0f9Sopenharmony_ci <td rowspan="2">go to daylight saving time</td> 874616d0f9Sopenharmony_ci</tr> 884616d0f9Sopenharmony_ci<tr> 894616d0f9Sopenharmony_ci <td rowspan="2">1922</td> 904616d0f9Sopenharmony_ci <td>1966</td> 914616d0f9Sopenharmony_ci <td>in April</td> 924616d0f9Sopenharmony_ci</tr> 934616d0f9Sopenharmony_ci<tr> 944616d0f9Sopenharmony_ci <td>1954</td> 954616d0f9Sopenharmony_ci <td>in September</td> 964616d0f9Sopenharmony_ci <td rowspan="2">return to standard time</td> 974616d0f9Sopenharmony_ci</tr> 984616d0f9Sopenharmony_ci<tr> 994616d0f9Sopenharmony_ci <td>1955</td> 1004616d0f9Sopenharmony_ci <td>1966</td> 1014616d0f9Sopenharmony_ci <td>in October</td> 1024616d0f9Sopenharmony_ci</tr> 1034616d0f9Sopenharmony_ci</table> 1044616d0f9Sopenharmony_ci 1054616d0f9Sopenharmony_ci<p>The <code>FROM</code> and <code>TO</code> columns, respectively, specify the 1064616d0f9Sopenharmony_cifirst and last calendar years defining a contiguous range over which a specific 1074616d0f9Sopenharmony_ciRule line is to apply. The keyword <code>only</code> can be used in the 1084616d0f9Sopenharmony_ci<code>TO</code> field to repeat the value of the <code>FROM</code> field in the 1094616d0f9Sopenharmony_cievent that a rule should only apply to a single year. Often, the keyword 1104616d0f9Sopenharmony_ci<code>max</code> is used to extend a rule’s application into the 1114616d0f9Sopenharmony_ciindefinite future; it is a platform-agnostic stand-in for the largest 1124616d0f9Sopenharmony_cirepresentable year. 1134616d0f9Sopenharmony_ci 1144616d0f9Sopenharmony_ci<p>The next column, <code>-</code>, is reserved; for compatibility with earlier 1154616d0f9Sopenharmony_cireleases, it always contains a hyphen, which acts as a kind of null value. 1164616d0f9Sopenharmony_ciPrior to the 2020b release, it was called the <code>TYPE</code> field, though 1174616d0f9Sopenharmony_ciit had not been used in the main data since the 2000e release. 1184616d0f9Sopenharmony_ciAn obsolescent supplementary file used the 1194616d0f9Sopenharmony_cifield as a proof-of-concept to allow <code>zic</code> to apply a given Rule 1204616d0f9Sopenharmony_ciline only to certain “types” of years within the specified range as 1214616d0f9Sopenharmony_cidictated by the output of a separate script, such as: only years which would 1224616d0f9Sopenharmony_cihave a US presidential election, or only years which wouldn’t. 1234616d0f9Sopenharmony_ci 1244616d0f9Sopenharmony_ci<p>The <code>SAVE</code> column contains the local (wall clock) offset from 1254616d0f9Sopenharmony_cilocal standard time. 1264616d0f9Sopenharmony_ciThis is usually either zero for standard time or one hour for daylight 1274616d0f9Sopenharmony_cisaving time; but there’s no reason, in principle, why it can’t 1284616d0f9Sopenharmony_citake on other values. 1294616d0f9Sopenharmony_ci 1304616d0f9Sopenharmony_ci<p>The <code>LETTER</code> (sometimes called <code>LETTER/S</code>) 1314616d0f9Sopenharmony_cicolumn can contain a variable 1324616d0f9Sopenharmony_cipart of the usual abbreviation of the time zone’s name, or it can just 1334616d0f9Sopenharmony_cibe a hyphen if there’s no variable part. For example, the abbreviation 1344616d0f9Sopenharmony_ciused in the central time zone will be either “CST” or 1354616d0f9Sopenharmony_ci“CDT”. The variable part is ‘S’ or ‘D’; 1364616d0f9Sopenharmony_ciand, sure enough, that’s just what we find in 1374616d0f9Sopenharmony_cithe <code>LETTER</code> column 1384616d0f9Sopenharmony_ciin the <code>Chicago</code> rules. More about this when we talk about 1394616d0f9Sopenharmony_ci“Zone” lines. 1404616d0f9Sopenharmony_ci 1414616d0f9Sopenharmony_ci<p>One important thing to notice is that “Rule” lines 1424616d0f9Sopenharmony_ciwant at once to be both <i>transitions</i> and <i>steady states</i>: 1434616d0f9Sopenharmony_ci<ul> 1444616d0f9Sopenharmony_ci<li>On the one hand, they represent transitions between standard and 1454616d0f9Sopenharmony_cidaylight saving time; and any number of Rule lines can be in effect 1464616d0f9Sopenharmony_ciduring a given period (which will always be a non-empty set of 1474616d0f9Sopenharmony_cicontiguous calendar years).</li> 1484616d0f9Sopenharmony_ci<li>On the other hand, the <code>SAVE</code> and <code>LETTER</code> 1494616d0f9Sopenharmony_cicolumns contain state that exists between transitions. More about this 1504616d0f9Sopenharmony_ciwhen we talk about the US rules.</li> 1514616d0f9Sopenharmony_ci</ul> 1524616d0f9Sopenharmony_ci 1534616d0f9Sopenharmony_ci<p>In the example above, the transition to daylight saving time 1544616d0f9Sopenharmony_cihappened on the 13<small><sup>th</sup></small> of June in 1920, and on 1554616d0f9Sopenharmony_cithe last Sunday in March in 1921; but the return to standard time 1564616d0f9Sopenharmony_cihappened on the last Sunday in October in both of those 1574616d0f9Sopenharmony_ciyears. Similarly, the rule for changing to daylight saving time was 1584616d0f9Sopenharmony_cithe same from 1922 to 1966; but the rule for returning to standard 1594616d0f9Sopenharmony_citime changed in 1955. Got it?</p> 1604616d0f9Sopenharmony_ci 1614616d0f9Sopenharmony_ci<p>OK, now for the somewhat more interesting “US” rules:</p> 1624616d0f9Sopenharmony_ci 1634616d0f9Sopenharmony_ci<table> 1644616d0f9Sopenharmony_ci<tr> 1654616d0f9Sopenharmony_ci <th colspan="6">From the Source File</th> 1664616d0f9Sopenharmony_ci</tr> 1674616d0f9Sopenharmony_ci<tr> 1684616d0f9Sopenharmony_ci <td colspan="6"> 1694616d0f9Sopenharmony_ci <table class="rule"> 1704616d0f9Sopenharmony_ci <tr><td style="border:none;text-align:left"> 1714616d0f9Sopenharmony_ci<pre class="td"> 1724616d0f9Sopenharmony_ci#Rule NAME FROM TO - IN ON AT SAVE LETTER/S 1734616d0f9Sopenharmony_ciRule US 1918 1919 - Mar lastSun 2:00 1:00 D 1744616d0f9Sopenharmony_ciRule US 1918 1919 - Oct lastSun 2:00 0 S 1754616d0f9Sopenharmony_ciRule US 1942 only - Feb 9 2:00 1:00 W # War 1764616d0f9Sopenharmony_ciRule US 1945 only - Aug 14 23:00u 1:00 P # Peace 1774616d0f9Sopenharmony_ciRule US 1945 only - Sep 30 2:00 0 S 1784616d0f9Sopenharmony_ciRule US 1967 2006 - Oct lastSun 2:00 0 S 1794616d0f9Sopenharmony_ciRule US 1967 1973 - Apr lastSun 2:00 1:00 D 1804616d0f9Sopenharmony_ciRule US 1974 only - Jan 6 2:00 1:00 D 1814616d0f9Sopenharmony_ciRule US 1975 only - Feb 23 2:00 1:00 D 1824616d0f9Sopenharmony_ciRule US 1976 1986 - Apr lastSun 2:00 1:00 D 1834616d0f9Sopenharmony_ciRule US 1987 2006 - Apr Sun>=1 2:00 1:00 D 1844616d0f9Sopenharmony_ciRule US 2007 max - Mar Sun>=8 2:00 1:00 D 1854616d0f9Sopenharmony_ciRule US 2007 max - Nov Sun>=1 2:00 0 S 1864616d0f9Sopenharmony_ci</pre> 1874616d0f9Sopenharmony_ci </td></tr></table></td> 1884616d0f9Sopenharmony_ci</tr> 1894616d0f9Sopenharmony_ci<tr> 1904616d0f9Sopenharmony_ci <th colspan="6">Reformatted a Bit</th> 1914616d0f9Sopenharmony_ci</tr> 1924616d0f9Sopenharmony_ci<tr> 1934616d0f9Sopenharmony_ci <th>From</th> 1944616d0f9Sopenharmony_ci <th>To</th> 1954616d0f9Sopenharmony_ci <th colspan="2">On</th> 1964616d0f9Sopenharmony_ci <th>At</th> 1974616d0f9Sopenharmony_ci <th>Action</th> 1984616d0f9Sopenharmony_ci</tr> 1994616d0f9Sopenharmony_ci<tr> 2004616d0f9Sopenharmony_ci <td rowspan="2">1918</td> 2014616d0f9Sopenharmony_ci <td rowspan="2">1919</td> 2024616d0f9Sopenharmony_ci <td rowspan="2">last Sunday</td> 2034616d0f9Sopenharmony_ci <td>in March</td> 2044616d0f9Sopenharmony_ci <td rowspan="3">02:00 local</td> 2054616d0f9Sopenharmony_ci <td>go to daylight saving time</td> 2064616d0f9Sopenharmony_ci</tr> 2074616d0f9Sopenharmony_ci<tr> 2084616d0f9Sopenharmony_ci <td>in October</td> 2094616d0f9Sopenharmony_ci <td>return to standard time</td> 2104616d0f9Sopenharmony_ci</tr> 2114616d0f9Sopenharmony_ci<tr> 2124616d0f9Sopenharmony_ci <td colspan="2">1942 only</td> 2134616d0f9Sopenharmony_ci <td colspan="2">February 9<small><sup>th</sup></small></td> 2144616d0f9Sopenharmony_ci <td>go to “war time”</td> 2154616d0f9Sopenharmony_ci</tr> 2164616d0f9Sopenharmony_ci<tr> 2174616d0f9Sopenharmony_ci <td colspan="2" rowspan="2">1945 only</td> 2184616d0f9Sopenharmony_ci <td colspan="2">August 14<small><sup>th</sup></small></td> 2194616d0f9Sopenharmony_ci <td>23:00 <a href="https://en.wikipedia.org/wiki/Universal_Time">UT</a></td> 2204616d0f9Sopenharmony_ci <td> 2214616d0f9Sopenharmony_ci rename “war time” to “peace<br>time;” 2224616d0f9Sopenharmony_ci clocks don’t change 2234616d0f9Sopenharmony_ci </td> 2244616d0f9Sopenharmony_ci</tr> 2254616d0f9Sopenharmony_ci<tr> 2264616d0f9Sopenharmony_ci <td colspan="2">September 30<small><sup>th</sup></small></td> 2274616d0f9Sopenharmony_ci <td rowspan="9">02:00 local</td> 2284616d0f9Sopenharmony_ci <td rowspan="2">return to standard time</td> 2294616d0f9Sopenharmony_ci</tr> 2304616d0f9Sopenharmony_ci<tr> 2314616d0f9Sopenharmony_ci <td rowspan="2">1967</td> 2324616d0f9Sopenharmony_ci <td>2006</td> 2334616d0f9Sopenharmony_ci <td rowspan="2">last Sunday</td> 2344616d0f9Sopenharmony_ci <td>in October</td> 2354616d0f9Sopenharmony_ci</tr> 2364616d0f9Sopenharmony_ci<tr> 2374616d0f9Sopenharmony_ci <td>1973</td> 2384616d0f9Sopenharmony_ci <td>in April</td> 2394616d0f9Sopenharmony_ci <td rowspan="6">go to daylight saving time</td> 2404616d0f9Sopenharmony_ci</tr> 2414616d0f9Sopenharmony_ci<tr> 2424616d0f9Sopenharmony_ci <td colspan="2">1974 only</td> 2434616d0f9Sopenharmony_ci <td colspan="2">January 6<small><sup>th</sup></small></td> 2444616d0f9Sopenharmony_ci</tr> 2454616d0f9Sopenharmony_ci<tr> 2464616d0f9Sopenharmony_ci <td colspan="2">1975 only</td> 2474616d0f9Sopenharmony_ci <td colspan="2">February 23<small><sup>rd</sup></small></td> 2484616d0f9Sopenharmony_ci</tr> 2494616d0f9Sopenharmony_ci<tr> 2504616d0f9Sopenharmony_ci <td>1976</td> 2514616d0f9Sopenharmony_ci <td>1986</td> 2524616d0f9Sopenharmony_ci <td>last Sunday</td> 2534616d0f9Sopenharmony_ci <td rowspan="2">in April</td> 2544616d0f9Sopenharmony_ci</tr> 2554616d0f9Sopenharmony_ci<tr> 2564616d0f9Sopenharmony_ci <td>1987</td> 2574616d0f9Sopenharmony_ci <td>2006</td> 2584616d0f9Sopenharmony_ci <td>first Sunday</td> 2594616d0f9Sopenharmony_ci</tr> 2604616d0f9Sopenharmony_ci<tr> 2614616d0f9Sopenharmony_ci <td rowspan="2">2007</td> 2624616d0f9Sopenharmony_ci <td rowspan="2">present</td> 2634616d0f9Sopenharmony_ci <td colspan="2">second Sunday in March</td> 2644616d0f9Sopenharmony_ci</tr> 2654616d0f9Sopenharmony_ci<tr> 2664616d0f9Sopenharmony_ci <td colspan="2">first Sunday in November</td> 2674616d0f9Sopenharmony_ci <td>return to standard time</td> 2684616d0f9Sopenharmony_ci</tr> 2694616d0f9Sopenharmony_ci</table> 2704616d0f9Sopenharmony_ci 2714616d0f9Sopenharmony_ci<p>There are two interesting things to note here.</p> 2724616d0f9Sopenharmony_ci 2734616d0f9Sopenharmony_ci<p>First, the time that something happens (in the <code>AT</code> 2744616d0f9Sopenharmony_cicolumn) is not necessarily the local (wall clock) time. The time can be 2754616d0f9Sopenharmony_cisuffixed with ‘s’ (for “standard”) to mean 2764616d0f9Sopenharmony_cilocal standard time, different from local (wall clock) time when observing 2774616d0f9Sopenharmony_cidaylight saving time; or it can be suffixed with ‘g’, 2784616d0f9Sopenharmony_ci‘u’, or ‘z’, all three of which mean the 2794616d0f9Sopenharmony_cistandard time at the 2804616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Prime_Meridian">prime meridian</a>. 2814616d0f9Sopenharmony_ci‘g’ stands for “<a 2824616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Greenwich_Mean_Time">GMT</a>”; 2834616d0f9Sopenharmony_ci‘u’ stands for “<a 2844616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Universal_Time">UT</a>” or “<a 2854616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">UTC</a>” 2864616d0f9Sopenharmony_ci(whichever was official at the time); ‘z’ stands for the 2874616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/Nautical_time">nautical time zone</a> 2884616d0f9Sopenharmony_ciZ (a.k.a. “Zulu” which, in turn, stands for ‘Z’). 2894616d0f9Sopenharmony_ciThe time can also be suffixed with ‘w’ meaning local (wall 2904616d0f9Sopenharmony_ciclock) time; but it usually isn’t because that’s the 2914616d0f9Sopenharmony_cidefault.</p> 2924616d0f9Sopenharmony_ci 2934616d0f9Sopenharmony_ci<p>Second, the day in the <code>ON</code> column, in addition to 2944616d0f9Sopenharmony_ci“<code>lastSun</code>” or a particular day of the month, 2954616d0f9Sopenharmony_cican have the form, “<code>Sun>=</code><i>x</i>” or 2964616d0f9Sopenharmony_ci“<code>Sun<=</code><i>x</i>,” where <i>x</i> is a day 2974616d0f9Sopenharmony_ciof the month. For example, “<code>Sun>=8</code>” means 2984616d0f9Sopenharmony_ci“the first Sunday on or after the eighth of the month,” in 2994616d0f9Sopenharmony_ciother words, the second Sunday of the month. Furthermore, although 3004616d0f9Sopenharmony_cithere are no examples above, the weekday needn’t be 3014616d0f9Sopenharmony_ci“<code>Sun</code>” in either form, but can be the usual 3024616d0f9Sopenharmony_cithree-character English abbreviation for any day of the week.</p> 3034616d0f9Sopenharmony_ci 3044616d0f9Sopenharmony_ci<p>And the US rules give us more examples of a couple of things 3054616d0f9Sopenharmony_cialready mentioned:</p> 3064616d0f9Sopenharmony_ci 3074616d0f9Sopenharmony_ci<ul> 3084616d0f9Sopenharmony_ci<li>The rules for changing to and from daylight saving time are 3094616d0f9Sopenharmony_ciactually <i>different sets</i> of rules; and the two sets can change 3104616d0f9Sopenharmony_ciindependently. Consider, for example, that the rule for the return to 3114616d0f9Sopenharmony_cistandard time stayed the same from 1967 to 2006; but the rule for the 3124616d0f9Sopenharmony_citransition to daylight saving time changed several times in the same 3134616d0f9Sopenharmony_ciperiod. There can also be periods, 1946 to 1966 for example, when no 3144616d0f9Sopenharmony_cirule from this group is in effect, and so either no transition 3154616d0f9Sopenharmony_cihappened in those years, or some other rule is in effect (perhaps a 3164616d0f9Sopenharmony_cistate or other more local rule).</li> 3174616d0f9Sopenharmony_ci 3184616d0f9Sopenharmony_ci<li>The <code>SAVE</code> and <code>LETTER</code> columns 3194616d0f9Sopenharmony_cicontain <i>steady state</i>, not transitions. Consider, for example, 3204616d0f9Sopenharmony_cithe transition from “war time” to “peace time” 3214616d0f9Sopenharmony_cithat happened on August 14, 1945. The “1:00” in 3224616d0f9Sopenharmony_cithe <code>SAVE</code> column is <i>not</i> an instruction to advance 3234616d0f9Sopenharmony_cithe clock an hour. It means that clocks should <i>be</i> one hour 3244616d0f9Sopenharmony_ciahead of standard time, which they already are because of the previous 3254616d0f9Sopenharmony_cirule, so there should be no change.</li> 3264616d0f9Sopenharmony_ci 3274616d0f9Sopenharmony_ci</ul> 3284616d0f9Sopenharmony_ci 3294616d0f9Sopenharmony_ci<p>OK, now let’s look at a Zone record:</p> 3304616d0f9Sopenharmony_ci 3314616d0f9Sopenharmony_ci<table> 3324616d0f9Sopenharmony_ci<tr> 3334616d0f9Sopenharmony_ci <th colspan="5">From the Source File</th> 3344616d0f9Sopenharmony_ci</tr> 3354616d0f9Sopenharmony_ci<tr> 3364616d0f9Sopenharmony_ci <td colspan="5"> 3374616d0f9Sopenharmony_ci <table class="rule"> 3384616d0f9Sopenharmony_ci <tr><td style="border:none;text-align:left"> 3394616d0f9Sopenharmony_ci<pre class="td"> 3404616d0f9Sopenharmony_ci#Zone NAME STDOFF RULES FORMAT [UNTIL] 3414616d0f9Sopenharmony_ciZone America/Chicago -5:50:36 - LMT 1883 Nov 18 12:09:24 3424616d0f9Sopenharmony_ci -6:00 US C%sT 1920 3434616d0f9Sopenharmony_ci -6:00 Chicago C%sT 1936 Mar 1 2:00 3444616d0f9Sopenharmony_ci -5:00 - EST 1936 Nov 15 2:00 3454616d0f9Sopenharmony_ci -6:00 Chicago C%sT 1942 3464616d0f9Sopenharmony_ci -6:00 US C%sT 1946 3474616d0f9Sopenharmony_ci -6:00 Chicago C%sT 1967 3484616d0f9Sopenharmony_ci -6:00 US C%sT 3494616d0f9Sopenharmony_ci</pre> 3504616d0f9Sopenharmony_ci </td></tr></table></td> 3514616d0f9Sopenharmony_ci</tr> 3524616d0f9Sopenharmony_ci<tr> 3534616d0f9Sopenharmony_ci <th colspan="5">Columns Renamed</th> 3544616d0f9Sopenharmony_ci</tr> 3554616d0f9Sopenharmony_ci<tr> 3564616d0f9Sopenharmony_ci <th rowspan="2">Standard Offset<br> 3574616d0f9Sopenharmony_ci from <a href="https://en.wikipedia.org/wiki/Prime_Meridian">Prime 3584616d0f9Sopenharmony_ci Meridian</a></th> 3594616d0f9Sopenharmony_ci <th rowspan="2">Daylight<br>Saving Time</th> 3604616d0f9Sopenharmony_ci <th rowspan="2">Abbreviation(s)</th> 3614616d0f9Sopenharmony_ci <th colspan="2">Ending at Local Time</th> 3624616d0f9Sopenharmony_ci</tr> 3634616d0f9Sopenharmony_ci<tr> 3644616d0f9Sopenharmony_ci <th>Date</th> 3654616d0f9Sopenharmony_ci <th>Time</th> 3664616d0f9Sopenharmony_ci</tr> 3674616d0f9Sopenharmony_ci<tr> 3684616d0f9Sopenharmony_ci <td>−5:50:36</td> 3694616d0f9Sopenharmony_ci <td>not observed</td> 3704616d0f9Sopenharmony_ci <td>LMT</td> 3714616d0f9Sopenharmony_ci <td>1883-11-18</td> 3724616d0f9Sopenharmony_ci <td>12:09:24</td> 3734616d0f9Sopenharmony_ci</tr> 3744616d0f9Sopenharmony_ci<tr> 3754616d0f9Sopenharmony_ci <td rowspan="2">−6:00:00</td> 3764616d0f9Sopenharmony_ci <td>US rules</td> 3774616d0f9Sopenharmony_ci <td rowspan="2">CST or CDT</td> 3784616d0f9Sopenharmony_ci <td>1920-01-01</td> 3794616d0f9Sopenharmony_ci <td>00:00:00</td> 3804616d0f9Sopenharmony_ci</tr> 3814616d0f9Sopenharmony_ci<tr> 3824616d0f9Sopenharmony_ci <td>Chicago rules</td> 3834616d0f9Sopenharmony_ci <td>1936-03-01</td> 3844616d0f9Sopenharmony_ci <td rowspan="2">02:00:00</td> 3854616d0f9Sopenharmony_ci</tr> 3864616d0f9Sopenharmony_ci<tr> 3874616d0f9Sopenharmony_ci <td>−5:00:00</td> 3884616d0f9Sopenharmony_ci <td>not observed</td> 3894616d0f9Sopenharmony_ci <td>EST</td> 3904616d0f9Sopenharmony_ci <td>1936-11-15</td> 3914616d0f9Sopenharmony_ci</tr> 3924616d0f9Sopenharmony_ci<tr> 3934616d0f9Sopenharmony_ci <td rowspan="4">−6:00:00</td> 3944616d0f9Sopenharmony_ci <td>Chicago rules</td> 3954616d0f9Sopenharmony_ci <td>CST or CDT</td> 3964616d0f9Sopenharmony_ci <td>1942-01-01</td> 3974616d0f9Sopenharmony_ci <td rowspan="3">00:00:00</td> 3984616d0f9Sopenharmony_ci</tr> 3994616d0f9Sopenharmony_ci<tr> 4004616d0f9Sopenharmony_ci <td>US rules</td> 4014616d0f9Sopenharmony_ci <td>CST, CWT or CPT</td> 4024616d0f9Sopenharmony_ci <td>1946-01-01</td> 4034616d0f9Sopenharmony_ci</tr> 4044616d0f9Sopenharmony_ci<tr> 4054616d0f9Sopenharmony_ci <td>Chicago rules</td> 4064616d0f9Sopenharmony_ci <td rowspan="2">CST or CDT</td> 4074616d0f9Sopenharmony_ci <td>1967-01-01</td> 4084616d0f9Sopenharmony_ci</tr> 4094616d0f9Sopenharmony_ci<tr> 4104616d0f9Sopenharmony_ci <td>US rules</td> 4114616d0f9Sopenharmony_ci <td colspan="2">—</td> 4124616d0f9Sopenharmony_ci</tr> 4134616d0f9Sopenharmony_ci</table> 4144616d0f9Sopenharmony_ci 4154616d0f9Sopenharmony_ci<p>There are a couple of interesting differences between Zones and Rules.</p> 4164616d0f9Sopenharmony_ci 4174616d0f9Sopenharmony_ci<p>First, and somewhat trivially, whereas Rules are considered to 4184616d0f9Sopenharmony_cicontain one or more records, a Zone is considered to be a single 4194616d0f9Sopenharmony_cirecord with zero or more <i>continuation lines</i>. Thus, the keyword, 4204616d0f9Sopenharmony_ci“<code>Zone</code>,” and the zone name are not 4214616d0f9Sopenharmony_cirepeated. The last line is the one without anything in 4224616d0f9Sopenharmony_cithe <code>[UNTIL]</code> column.</p> 4234616d0f9Sopenharmony_ci 4244616d0f9Sopenharmony_ci<p>Second, and more fundamentally, each line of a Zone represents a 4254616d0f9Sopenharmony_cisteady state, not a transition between states. The state exists from 4264616d0f9Sopenharmony_cithe date and time in the previous line’s <code>[UNTIL]</code> 4274616d0f9Sopenharmony_cicolumn up to the date and time in the current 4284616d0f9Sopenharmony_ciline’s <code>[UNTIL]</code> column. In other words, the date and 4294616d0f9Sopenharmony_citime in the <code>[UNTIL]</code> column is the instant that separates 4304616d0f9Sopenharmony_cithis state from the next. Where that would be ambiguous because 4314616d0f9Sopenharmony_ciwe’re setting our clocks back, the <code>[UNTIL]</code> column 4324616d0f9Sopenharmony_cispecifies the first occurrence of the instant. The state specified by 4334616d0f9Sopenharmony_cithe last line, the one without anything in the <code>[UNTIL]</code> 4344616d0f9Sopenharmony_cicolumn, continues to the present.</p> 4354616d0f9Sopenharmony_ci 4364616d0f9Sopenharmony_ci<p>The first line typically specifies the mean solar time observed 4374616d0f9Sopenharmony_cibefore the introduction of standard time. Since there’s no line before 4384616d0f9Sopenharmony_cithat, it has no beginning. <code>8-) </code> For some places near the <a 4394616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/International_Date_Line">International 4404616d0f9Sopenharmony_ciDate Line</a>, the first <i>two</i> lines will show solar times 4414616d0f9Sopenharmony_cidiffering by 24 hours; this corresponds to a movement of the Date 4424616d0f9Sopenharmony_ciLine. For example:</p> 4434616d0f9Sopenharmony_ci 4444616d0f9Sopenharmony_ci<pre> 4454616d0f9Sopenharmony_ci#Zone NAME STDOFF RULES FORMAT [UNTIL] 4464616d0f9Sopenharmony_ciZone America/Juneau 15:02:19 - LMT 1867 Oct 18 4474616d0f9Sopenharmony_ci -8:57:41 - LMT ... 4484616d0f9Sopenharmony_ci</pre> 4494616d0f9Sopenharmony_ci 4504616d0f9Sopenharmony_ci<p>When Alaska was purchased from Russia in 1867, the Date Line moved 4514616d0f9Sopenharmony_cifrom the Alaska/Canada border to the Bering Strait; and the time in 4524616d0f9Sopenharmony_ciAlaska was then 24 hours earlier than it had 4534616d0f9Sopenharmony_cibeen. <code><aside></code>(6 October in the Julian calendar, 4544616d0f9Sopenharmony_ciwhich Russia was still using then for religious reasons, was followed 4554616d0f9Sopenharmony_ciby <i>a second instance of the same day with a different name</i>, 18 4564616d0f9Sopenharmony_ciOctober in the Gregorian calendar. Isn’t civil time 4574616d0f9Sopenharmony_ciwonderful? <code>8-)</code>)<code></aside></code></p> 4584616d0f9Sopenharmony_ci 4594616d0f9Sopenharmony_ci<p>The abbreviation, “LMT” stands for “local mean 4604616d0f9Sopenharmony_citime”, which is an invention of 4614616d0f9Sopenharmony_cithe <a href="https://en.wikipedia.org/wiki/Tz_database">tz 4624616d0f9Sopenharmony_cidatabase</a> and was probably never actually used during the 4634616d0f9Sopenharmony_ciperiod. Furthermore, the value is almost certainly wrong except in the 4644616d0f9Sopenharmony_ciarchetypal place after which the zone is named. (The tz database 4654616d0f9Sopenharmony_ciusually doesn’t provide a separate Zone record for places where 4664616d0f9Sopenharmony_cinothing significant happened after 1970.)</p> 4674616d0f9Sopenharmony_ci 4684616d0f9Sopenharmony_ci<p>The <code>RULES</code> column tells us whether daylight saving time is being observed: 4694616d0f9Sopenharmony_ci<ul> 4704616d0f9Sopenharmony_ci<li>A hyphen, a kind of null value, means that we have not set our 4714616d0f9Sopenharmony_ciclocks ahead of standard time.</li> 4724616d0f9Sopenharmony_ci 4734616d0f9Sopenharmony_ci<li>An amount of time (usually but not necessarily “1:00” 4744616d0f9Sopenharmony_cimeaning one hour) means that we have set our clocks ahead by that 4754616d0f9Sopenharmony_ciamount.</li> 4764616d0f9Sopenharmony_ci 4774616d0f9Sopenharmony_ci<li>Some alphabetic string means that we <i>might have</i> set our 4784616d0f9Sopenharmony_ciclocks ahead; and we need to check the rule the name of which is the 4794616d0f9Sopenharmony_cigiven alphabetic string.</li> 4804616d0f9Sopenharmony_ci</ul> 4814616d0f9Sopenharmony_ci 4824616d0f9Sopenharmony_ci<p>An example of a specific amount of time is:</p> 4834616d0f9Sopenharmony_ci<pre> 4844616d0f9Sopenharmony_ci#Zone NAME STDOFF RULES FORMAT [UNTIL] 4854616d0f9Sopenharmony_ciZone Pacific/Honolulu ... 1933 Apr 30 2:00 4864616d0f9Sopenharmony_ci -10:30 1:00 HDT 1933 May 21 12:00 4874616d0f9Sopenharmony_ci ... 4884616d0f9Sopenharmony_ci</pre> 4894616d0f9Sopenharmony_ci 4904616d0f9Sopenharmony_ci<p>Hawaii tried daylight saving time for three weeks in 1933 and 4914616d0f9Sopenharmony_cidecided they didn’t like it. <code>8-) </code>Note that 4924616d0f9Sopenharmony_cithe <code>STDOFF</code> column always contains the standard time 4934616d0f9Sopenharmony_cioffset, so the local (wall clock) time during this period was GMT − 4944616d0f9Sopenharmony_ci10:30 + 1:00 = GMT − 9:30.</p> 4954616d0f9Sopenharmony_ci 4964616d0f9Sopenharmony_ci<p>The <code>FORMAT</code> column specifies the usual abbreviation of 4974616d0f9Sopenharmony_cithe time zone name. It should have one of four forms:</p> 4984616d0f9Sopenharmony_ci<ul> 4994616d0f9Sopenharmony_ci 5004616d0f9Sopenharmony_ci<li>a time zone abbreviation that is a string of three or more 5014616d0f9Sopenharmony_cicharacters that are either ASCII alphanumerics, 5024616d0f9Sopenharmony_ci“<code>+</code>”, or “<code>-</code>”</li> 5034616d0f9Sopenharmony_ci 5044616d0f9Sopenharmony_ci<li>the string “%z”, in which case the 5054616d0f9Sopenharmony_ci“<code>%z</code>” will be replaced by a numeric time zone 5064616d0f9Sopenharmony_ciabbreviation</li> 5074616d0f9Sopenharmony_ci 5084616d0f9Sopenharmony_ci<li>a pair of time zone abbreviations separated by a slash 5094616d0f9Sopenharmony_ci(‘<code>/</code>’), in which case the first string is the 5104616d0f9Sopenharmony_ciabbreviation for the standard time name and the second string is the 5114616d0f9Sopenharmony_ciabbreviation for the daylight saving time name</li> 5124616d0f9Sopenharmony_ci 5134616d0f9Sopenharmony_ci<li>a string containing “<code>%s</code>”, in which case 5144616d0f9Sopenharmony_cithe “<code>%s</code>” will be replaced by the text in the 5154616d0f9Sopenharmony_ciappropriate Rule’s <code>LETTER</code> column, and the resulting 5164616d0f9Sopenharmony_cistring should be a time zone abbreviation</li> 5174616d0f9Sopenharmony_ci</ul> 5184616d0f9Sopenharmony_ci 5194616d0f9Sopenharmony_ci<p>The last two make sense only if there’s a named rule in effect.</p> 5204616d0f9Sopenharmony_ci 5214616d0f9Sopenharmony_ci<p>An example of a slash is:</p> 5224616d0f9Sopenharmony_ci<pre> 5234616d0f9Sopenharmony_ci#Zone NAME STDOFF RULES FORMAT [UNTIL] 5244616d0f9Sopenharmony_ciZone Europe/London ... 1996 5254616d0f9Sopenharmony_ci 0:00 EU GMT/BST 5264616d0f9Sopenharmony_ci</pre> 5274616d0f9Sopenharmony_ci 5284616d0f9Sopenharmony_ci<p>The current time in the UK is called either Greenwich mean time or 5294616d0f9Sopenharmony_ciBritish summer time.</p> 5304616d0f9Sopenharmony_ci 5314616d0f9Sopenharmony_ci<p>One wrinkle, not fully explained in <code>zic.8.txt</code>, is what 5324616d0f9Sopenharmony_cihappens when switching to a named rule. To what values should 5334616d0f9Sopenharmony_cithe <code>SAVE</code> and <code>LETTER</code> data be initialized?</p> 5344616d0f9Sopenharmony_ci 5354616d0f9Sopenharmony_ci<ul> 5364616d0f9Sopenharmony_ci<li>If at least one transition has happened, use 5374616d0f9Sopenharmony_cithe <code>SAVE</code> and <code>LETTER</code> data from the most 5384616d0f9Sopenharmony_cirecent.</li> 5394616d0f9Sopenharmony_ci 5404616d0f9Sopenharmony_ci<li>If switching to a named rule before any transition has happened, 5414616d0f9Sopenharmony_ciassume standard time (<code>SAVE</code> zero), and use 5424616d0f9Sopenharmony_cithe <code>LETTER</code> data from the earliest transition with 5434616d0f9Sopenharmony_cia <code>SAVE</code> of zero. 5444616d0f9Sopenharmony_ci 5454616d0f9Sopenharmony_ci</ul> 5464616d0f9Sopenharmony_ci 5474616d0f9Sopenharmony_ci<p>And three last things about the <code>FORMAT</code> column:</p> 5484616d0f9Sopenharmony_ci<ul> 5494616d0f9Sopenharmony_ci 5504616d0f9Sopenharmony_ci<li>The <a href="https://en.wikipedia.org/wiki/Tz_database">tz 5514616d0f9Sopenharmony_cidatabase</a> gives abbreviations for time zones 5524616d0f9Sopenharmony_ciin popular English-language usage. For 5534616d0f9Sopenharmony_ciexample, the last line in 5544616d0f9Sopenharmony_ci<code>Zone</code> <code>Pacific/Honolulu</code> (shown below) gives 5554616d0f9Sopenharmony_ci“HST” for “Hawaii standard time” even though the 5564616d0f9Sopenharmony_ci<a href="https://www.law.cornell.edu/uscode/text/15/263">legal</a> 5574616d0f9Sopenharmony_ciname for that time zone is “Hawaii-Aleutian standard time.” 5584616d0f9Sopenharmony_ciThis author has read that there are also some places in Australia where 5594616d0f9Sopenharmony_cipopular time zone names differ from the legal ones. 5604616d0f9Sopenharmony_ci 5614616d0f9Sopenharmony_ci<li>No attempt is made to <a 5624616d0f9Sopenharmony_cihref="https://en.wikipedia.org/wiki/Internationalization_and_localization">localize</a> 5634616d0f9Sopenharmony_cithe abbreviations. They are intended to be the values returned through the 5644616d0f9Sopenharmony_ci<code>"%Z"</code> format specifier to 5654616d0f9Sopenharmony_ci<a href="https://en.wikipedia.org/wiki/C_(programming_language)">C</a>’s 5664616d0f9Sopenharmony_ci<a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/strftime.html"><code>strftime</code></a> 5674616d0f9Sopenharmony_cifunction in the 5684616d0f9Sopenharmony_ci<a href="https://kirste.userpage.fu-berlin.de/chemnet/use/info/libc/libc_19.html#SEC324">“C” locale</a>. 5694616d0f9Sopenharmony_ci 5704616d0f9Sopenharmony_ci<li>If there is no generally accepted abbreviation for a time zone, 5714616d0f9Sopenharmony_cia numeric offset is used instead, e.g., <code>+07</code> for 7 hours 5724616d0f9Sopenharmony_ciahead of Greenwich. By convention, <code>-00</code> is used in a 5734616d0f9Sopenharmony_cizone while uninhabited, where the offset is zero but in some sense 5744616d0f9Sopenharmony_cithe true offset is undefined. 5754616d0f9Sopenharmony_ci</ul> 5764616d0f9Sopenharmony_ci 5774616d0f9Sopenharmony_ci<p>As a final example, here’s the complete history for Hawaii:</p> 5784616d0f9Sopenharmony_ci 5794616d0f9Sopenharmony_ci<table> 5804616d0f9Sopenharmony_ci<tr> 5814616d0f9Sopenharmony_ci <th colspan="6">Relevant Excerpts from the US Rules</th> 5824616d0f9Sopenharmony_ci</tr> 5834616d0f9Sopenharmony_ci<tr> 5844616d0f9Sopenharmony_ci <td colspan="6"> 5854616d0f9Sopenharmony_ci <table class="rule"> 5864616d0f9Sopenharmony_ci <tr><td style="border:none;text-align:left"> 5874616d0f9Sopenharmony_ci<pre class="td"> 5884616d0f9Sopenharmony_ci#Rule NAME FROM TO - IN ON AT SAVE LETTER/S 5894616d0f9Sopenharmony_ciRule US 1918 1919 - Oct lastSun 2:00 0 S 5904616d0f9Sopenharmony_ciRule US 1942 only - Feb 9 2:00 1:00 W # War 5914616d0f9Sopenharmony_ciRule US 1945 only - Aug 14 23:00u 1:00 P # Peace 5924616d0f9Sopenharmony_ciRule US 1945 only - Sep lastSun 2:00 0 S 5934616d0f9Sopenharmony_ci</pre> 5944616d0f9Sopenharmony_ci </td></tr></table></td> 5954616d0f9Sopenharmony_ci</tr> 5964616d0f9Sopenharmony_ci<tr> 5974616d0f9Sopenharmony_ci <th colspan="6">The Zone Record</th> 5984616d0f9Sopenharmony_ci</tr> 5994616d0f9Sopenharmony_ci<tr> 6004616d0f9Sopenharmony_ci <td colspan="6"> 6014616d0f9Sopenharmony_ci <table class="rule"> 6024616d0f9Sopenharmony_ci <tr><td style="border:none;text-align:left"> 6034616d0f9Sopenharmony_ci<pre class="td"> 6044616d0f9Sopenharmony_ci#Zone NAME STDOFF RULES FORMAT [UNTIL] 6054616d0f9Sopenharmony_ciZone Pacific/Honolulu -10:31:26 - LMT 1896 Jan 13 12:00 6064616d0f9Sopenharmony_ci -10:30 - HST 1933 Apr 30 2:00 6074616d0f9Sopenharmony_ci -10:30 1:00 HDT 1933 May 21 2:00 6084616d0f9Sopenharmony_ci -10:30 US H%sT 1947 Jun 8 2:00 6094616d0f9Sopenharmony_ci -10:00 - HST 6104616d0f9Sopenharmony_ci</pre> 6114616d0f9Sopenharmony_ci </td></tr></table></td> 6124616d0f9Sopenharmony_ci</tr> 6134616d0f9Sopenharmony_ci<tr> 6144616d0f9Sopenharmony_ci <th colspan="6">What We Infer</th> 6154616d0f9Sopenharmony_ci</tr> 6164616d0f9Sopenharmony_ci<tr> 6174616d0f9Sopenharmony_ci <th rowspan="2">Wall-Clock<br>Offset from<br>Prime Meridian</th> 6184616d0f9Sopenharmony_ci <th rowspan="2">Adjust<br>Clocks</th> 6194616d0f9Sopenharmony_ci <th colspan="2">Time Zone</th> 6204616d0f9Sopenharmony_ci <th colspan="2">Ending at Local Time</th> 6214616d0f9Sopenharmony_ci</tr> 6224616d0f9Sopenharmony_ci<tr> 6234616d0f9Sopenharmony_ci <th>Abbrv.</th> 6244616d0f9Sopenharmony_ci <th>Name</th> 6254616d0f9Sopenharmony_ci <th>Date</th> 6264616d0f9Sopenharmony_ci <th>Time</th> 6274616d0f9Sopenharmony_ci</tr> 6284616d0f9Sopenharmony_ci<tr> 6294616d0f9Sopenharmony_ci <td>−10:31:26</td> 6304616d0f9Sopenharmony_ci <td>—</td> 6314616d0f9Sopenharmony_ci <td>LMT</td> 6324616d0f9Sopenharmony_ci <td>local mean time</td> 6334616d0f9Sopenharmony_ci <td>1896-01-13</td> 6344616d0f9Sopenharmony_ci <td>12:00</td> 6354616d0f9Sopenharmony_ci</tr> 6364616d0f9Sopenharmony_ci<tr> 6374616d0f9Sopenharmony_ci <td>−10:30</td> 6384616d0f9Sopenharmony_ci <td>+0:01:26</td> 6394616d0f9Sopenharmony_ci <td>HST</td> 6404616d0f9Sopenharmony_ci <td>Hawaii standard time</td> 6414616d0f9Sopenharmony_ci <td>1933-04-30</td> 6424616d0f9Sopenharmony_ci <td>02:00</td> 6434616d0f9Sopenharmony_ci</tr> 6444616d0f9Sopenharmony_ci<tr> 6454616d0f9Sopenharmony_ci <td>−9:30</td> 6464616d0f9Sopenharmony_ci <td>+1:00</td> 6474616d0f9Sopenharmony_ci <td>HDT</td> 6484616d0f9Sopenharmony_ci <td>Hawaii daylight time</td> 6494616d0f9Sopenharmony_ci <td>1933-05-21</td> 6504616d0f9Sopenharmony_ci <td>12:00</td> 6514616d0f9Sopenharmony_ci</tr> 6524616d0f9Sopenharmony_ci<tr> 6534616d0f9Sopenharmony_ci <td>−10:30¹</td> 6544616d0f9Sopenharmony_ci <td>−1:00¹</td> 6554616d0f9Sopenharmony_ci <td>HST¹</td> 6564616d0f9Sopenharmony_ci <td>Hawaii standard time</td> 6574616d0f9Sopenharmony_ci <td>1942-02-09</td> 6584616d0f9Sopenharmony_ci <td>02:00</td> 6594616d0f9Sopenharmony_ci</tr> 6604616d0f9Sopenharmony_ci<tr> 6614616d0f9Sopenharmony_ci <td rowspan="2">−9:30</td> 6624616d0f9Sopenharmony_ci <td>+1:00</td> 6634616d0f9Sopenharmony_ci <td>HWT</td> 6644616d0f9Sopenharmony_ci <td>Hawaii war time</td> 6654616d0f9Sopenharmony_ci <td>1945-08-14</td> 6664616d0f9Sopenharmony_ci <td>13:30²</td> 6674616d0f9Sopenharmony_ci</tr> 6684616d0f9Sopenharmony_ci<tr> 6694616d0f9Sopenharmony_ci <td>0</td> 6704616d0f9Sopenharmony_ci <td>HPT</td> 6714616d0f9Sopenharmony_ci <td>Hawaii peace time</td> 6724616d0f9Sopenharmony_ci <td>1945-09-30</td> 6734616d0f9Sopenharmony_ci <td rowspan="2">02:00</td> 6744616d0f9Sopenharmony_ci</tr> 6754616d0f9Sopenharmony_ci<tr> 6764616d0f9Sopenharmony_ci <td>−10:30</td> 6774616d0f9Sopenharmony_ci <td>−1:00</td> 6784616d0f9Sopenharmony_ci <td rowspan="2">HST</td> 6794616d0f9Sopenharmony_ci <td rowspan="2">Hawaii standard time</td> 6804616d0f9Sopenharmony_ci <td>1947-06-08</td> 6814616d0f9Sopenharmony_ci</tr> 6824616d0f9Sopenharmony_ci<tr> 6834616d0f9Sopenharmony_ci <td>−10:00³</td> 6844616d0f9Sopenharmony_ci <td>+0:30³</td> 6854616d0f9Sopenharmony_ci <td colspan="2">—</td> 6864616d0f9Sopenharmony_ci</tr> 6874616d0f9Sopenharmony_ci<tr> 6884616d0f9Sopenharmony_ci <td colspan="6" class="footnote"> 6894616d0f9Sopenharmony_ci ¹Switching to US rules…most recent transition (in 1919) was to standard time 6904616d0f9Sopenharmony_ci </td> 6914616d0f9Sopenharmony_ci</tr> 6924616d0f9Sopenharmony_ci<tr> 6934616d0f9Sopenharmony_ci <td colspan="6" class="footnote"> 6944616d0f9Sopenharmony_ci ²23:00 <a href="https://en.wikipedia.org/wiki/Universal_Time">UT</a> 6954616d0f9Sopenharmony_ci + (−9:30) = 13:30 local 6964616d0f9Sopenharmony_ci </td> 6974616d0f9Sopenharmony_ci</tr> 6984616d0f9Sopenharmony_ci<tr> 6994616d0f9Sopenharmony_ci <td colspan="6" class="footnote"> 7004616d0f9Sopenharmony_ci ³Since <a href="https://en.wikipedia.org/wiki/ISO_8601">1947–06–08T12:30Z</a>, 7014616d0f9Sopenharmony_ci the civil time in Hawaii has been 7024616d0f9Sopenharmony_ci <a href="https://en.wikipedia.org/wiki/Universal_Time">UT</a>/<a href="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">UTC</a> 7034616d0f9Sopenharmony_ci − 10:00 year-round. 7044616d0f9Sopenharmony_ci </td> 7054616d0f9Sopenharmony_ci</tr> 7064616d0f9Sopenharmony_ci</table> 7074616d0f9Sopenharmony_ci 7084616d0f9Sopenharmony_ci<p>There will be a short quiz later. <code>8-)</code></p> 7094616d0f9Sopenharmony_ci 7104616d0f9Sopenharmony_ci<hr> 7114616d0f9Sopenharmony_ci<address> 7124616d0f9Sopenharmony_ciThis web page is in the public domain, so clarified as of 7134616d0f9Sopenharmony_ci2015-10-20 by Bill Seymour. 7144616d0f9Sopenharmony_ci<br> 7154616d0f9Sopenharmony_ciAll suggestions and corrections will be welcome; all flames will be amusing. 7164616d0f9Sopenharmony_ciMail to was at pobox dot com. 7174616d0f9Sopenharmony_ci</address> 7184616d0f9Sopenharmony_ci</body> 7194616d0f9Sopenharmony_ci</html> 720