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<?xml version="1.0" encoding="US-ASCII"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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"DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<title>Sources for Time Zone and Daylight Saving Time Data</title>
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<link rel="schema.DC" href="http://purl.org/DC/elements/1.1/" />
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<meta http-equiv="Content-type" content='text/html; charset="US-ASCII"' />
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<meta name="DC.Creator" content="Eggert, Paul" />
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<meta name="DC.Contributor" content="Olson, Arthur David" />
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<meta name="DC.Date" content="2004-05-24" />
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<meta name="DC.Description"
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content="Sources of information about time zones and daylight saving time" />
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<meta name="DC.Identifier" content="http://www.twinsun.com/tz/tz-link.htm" />
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<meta name="Keywords"
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content="database,daylight saving,DST,time zone,timezone,tz,zoneinfo" />
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</head>
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<body>
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<h1>Sources for Time Zone and Daylight Saving Time Data</h1>
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<address>
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@(#)tz-link.htm 7.42
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</address>
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<p>
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Please send corrections to this web page to the
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<a href="mailto:tz@elsie.nci.nih.gov">time zone mailing list</a>.
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</p>
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<h2>The <code>tz</code> database</h2>
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<p>
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The public-domain time zone database contains code and data
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that represent the history of local time
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for many representative locations around the globe.
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It is updated periodically to reflect changes made by political bodies
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to UTC offsets and daylight-saving rules.
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This database (often called <code>tz</code> or <code>zoneinfo</code>)
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is used by several implementations,
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including
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<a href="http://www.gnu.org/software/libc/">the GNU C Library</a> used in
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<a href="http://www.linux.org/">GNU/Linux</a>,
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<a href="http://www.freebsd.org/">FreeBSD</a>,
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<a href="http://www.netbsd.org/">NetBSD</a>,
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<a href="http://www.openbsd.org/">OpenBSD</a>,
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<a href="http://www.cygwin.com/">Cygwin</a>,
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<a href="http://www.delorie.com/djgpp/">DJGPP</a>,
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<a href="http://www.hp.com/products1/unix/operating/">HP-UX</a>,
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<a href="http://www.sgi.com/developers/technology/irix/">IRIX</a>,
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<a href="http://www.apple.com/macosx/">Mac OS X</a>,
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<a href="http://h71000.www7.hp.com/">OpenVMS</a>,
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<a href="http://wwws.sun.com/software/solaris/">Solaris</a>,
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<a href="http://www.tru64unix.compaq.com/">Tru64</a>, and
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<a href="http://www.sco.com/products/unixware/">UnixWare</a>.</p>
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<p>
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Each location in the database represents a national region where all
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clocks keeping local time have agreed since 1970.
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Locations are identified by continent or ocean and then by the name of
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the location, which is typically the largest city within the region.
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For example, <code>America/New_York</code>
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represents most of the US eastern time zone;
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<code>America/Indianapolis</code> represents most of Indiana, which
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uses eastern time without daylight saving time (DST);
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<code>America/Detroit</code> represents most of Michigan, which uses
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eastern time but with different DST rules in 1975;
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and other entries represent smaller regions like Starke County,
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Kentucky, which switched from central to eastern time in 1991.
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To use the database, set the <code>TZ</code> environment variable to
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the location's full name, e.g., <code>TZ="America/New_York"</code>.</p>
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<p>
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In the <code>tz</code> database's
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<a href="ftp://elsie.nci.nih.gov/pub/">FTP distribution</a>,
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the code is in the file <code>tzcode<var>C</var>.tar.gz</code>,
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where <code><var>C</var></code> is the code's version;
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similarly, the data are in <code>tzdata<var>D</var>.tar.gz</code>,
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where <code><var>D</var></code> is the data's version.
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The following shell commands download
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these files to a GNU/Linux or similar host; see the downloaded
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<code>README</code> file for what to do next.</p>
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<pre style="margin-left: 2em"><code><a href="http://www.gnu.org/software/wget/">wget</a> 'ftp://elsie.nci.nih.gov/pub/tz*.tar.gz'
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<a href="http://www.gnu.org/software/gzip/">gzip</a> -dc tzcode*.tar.gz | <a href="http://www.gnu.org/software/tar/">tar</a> -xf -
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gzip -dc tzdata*.tar.gz | tar -xf -
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</code></pre>
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<p>
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The code lets you compile the <code>tz</code> source files into
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machine-readable binary files, one for each location. It also lets
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you read a <code>tz</code> binary file and interpret time stamps for that
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location.</p>
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<p>
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The data are by no means authoritative. If you find errors, please
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send changes to the <a href="mailto:tz@elsie.nci.nih.gov">time zone
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mailing list</a>. You can also <a
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href="mailto:tz-request@elsie.nci.nih.gov">subscribe</a> to the
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mailing list, retrieve the <a
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href="ftp://elsie.nci.nih.gov/pub/tzarchive.gz">archive of old
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messages</a> (in gzip compressed format), or retrieve <a
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href="ftp://munnari.oz.au/pub/oldtz/">archived older versions of code
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and data</a>.</p>
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<p>
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The Web has several other sources for time zone and daylight saving time data.
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Here are some recent links that may be of interest.
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</p>
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<h2>Web pages using recent versions of the <code>tz</code> database</h2>
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<ul>
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<li><a href="http://twiki.org/cgi-bin/xtra/tzdate">Date and Time Gateway</a>
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is a text-based point-and-click interface to tables of current time
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throughout the world.</li>
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<li>Fancier web interfaces, roughly in ascending order of complexity, include:
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<ul>
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<li><a href="http://www.hilink.com.au/times/">Local Times Around the
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World</a></li>
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<li><a href="http://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current Time in 1000 Places</a></li>
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<li><a href="http://timezoneconverter.com/">Time Zone Converter</a></li>
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</ul></li>
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<li><a href="http://www.holidayfestival.com/">The Worldwide Holiday
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& Festival Site</a> lists DST-related clock changes along with
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holidays.</li>
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<li><a href="http://www.timeanddate.com/worldclock/">The World Clock -
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Time Zones</a>
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is a web interface to a time zone database derived from
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<code>tz</code>'s.</li>
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</ul>
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<h2>Other time zone database formats</h2>
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<ul>
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<li>The <a href="ftp://ftp.rfc-editor.org/in-notes/rfc2445.txt">
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Internet Calendaring and Scheduling Core Object Specification
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(iCalendar)</a> specification published by the <a
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href="http://www.ietf.org/html.charters/calsch-charter.html">IETF
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Calendaring and Scheduling Working Group (calsch)</a> covers time zone
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data; see its VTIMEZONE calendar component.</li>
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<li>The <a
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href="http://lists.w3.org/Archives/Public/www-rdf-calendar/">www-rdf-calendar</a>
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list discusses <a href="http://www.w3.org/RDF/">RDF</a>-based calendar
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and group scheduling systems, and has a <a
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href="http://www.w3.org/2002/12/cal/#tzd">workspace on time zone
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data</a> converted from <code>tz</code>. An earlier <a
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href="http://www.w3.org/2000/01/foo">schema</a> was sketched out by <a
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href="http://www.w3.org/People/Berners-Lee/">Tim Berners-Lee</a>.</li>
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<li><a
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href="http://www.calsch.org/ietf/archives/draft-ietf-calsch-many-xcal-02.txt">XCal</a>
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was a draft <a href="http://www.w3.org/XML/">XML</a> document type
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definition that corresponded to iCalendar.</li>
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</ul>
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<h2>Other <code>tz</code> compilers</h2>
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<ul>
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<li><a href="http://www.dachaplin.dsl.pipex.com/vzic">Vzic iCalendar
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Timezone Converter</a> describes a program Vzic that compiles
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<code>tz</code> source into iCalendar-compatible VTIMEZONE files.
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Vzic is freely
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available under the <a href="http://www.gnu.org/copyleft/gpl.html">GNU
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General Public License (GPL)</a>.</li>
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<li><a
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href="http://search.cpan.org/dist/DateTime-TimeZone/">DateTime::TimeZone</a>
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contains a script <code>parse_olson</code> that compiles
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<code>tz</code> source into <a href="http://www.perl.org/">Perl</a>
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modules. It is part of the Perl <a
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href="http://datetime.perl.org/">DateTime Project</a>, which is freely
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available under both the GPL and the Perl <a
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href="http://www.perl.com/language/misc/Artistic.html">Artistic
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License</a>. DateTime::TimeZone also contains a script
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<code>tests_from_zdump</code> that generates test cases for each clock
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transition in the <code>tz</code> database.</li>
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<li><a href="http://oss.software.ibm.com/icu/">International Components for
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Unicode (ICU)</a> contains a C/C++ library for internationalization that
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has a compiler from <samp>tz</samp> source into an ICU-specific format.
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ICU is freely available under a BSD-style license.</li>
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<li><a href="http://joda-time.sourceforge.net/">Joda Time - Java date
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and time API</a> contains a class
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<code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles
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<code>tz</code> source into a Joda-specific binary format. Joda Time
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is freely available under a BSD-style license.</li>
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</ul>
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<h2>Other <code>tz</code> binary file readers</h2>
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<ul>
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<li>The <a href="http://www.gnu.org/software/libc/">GNU C Library</a>
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has an independent, thread-safe implementation of
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a <code>tz</code> binary file reader.
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This library is freely available under the
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<a href="http://www.gnu.org/copyleft/lesser.html">
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GNU Lesser General Public License (LGPL)</a>,
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and is widely used in GNU/Linux systems.</li>
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<li><a href="http://www.bmsi.com/java/#TZ">ZoneInfo.java</a>
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is a <code>tz</code> binary file reader written in Java.
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It is freely available under the GNU LGPL.</li>
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<li><a href="http://s.keim.free.fr/tz/doc.html">Python time zones</a>
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is a <code>tz</code> binary file reader written in <a
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href="http://www.python.org/">Python</a>. It is freely available
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under a BSD-style license.</li>
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</ul>
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<h2>Other <code>tz</code>-based time zone conversion software</h2>
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<ul>
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<li><a href="http://java.sun.com/">Sun Java</a> releases since 1.4
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contain a copy of a recent <samp>tz</samp> database in a Java-specific
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format.</li>
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<li><a
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href="http://www1.tip.nl/~t876506/AboutTimeZonesHC.html">HyperCard
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time zones calculator</a> is a HyperCard stack.</li>
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<li><a
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href="http://www.cimmyt.org/timezone/">World Time Explorer</a> is a
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Microsoft Windows program.</li>
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</ul>
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<h2>Other time zone databases</h2>
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<ul>
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<li><a href="http://www.astro.com/cgi-bin/atlw3/aq.cgi?lang=e">Atlas Query
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- Astrodienst</a> is Astrodienst's Web version of Shanks's
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excellent time zone history atlases published in both <a
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href="http://astrocom.com/software/pcatlas.php">computer</a> and <a
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href="http://astrocom.com/books/xrefa.php#SHANKS">book</a> form by <a
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href="http://astrocom.com/">Astro Communications Services</a>.</li>
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<li><a href="http://worldtime.com/">WORLDTIME: interactive atlas,
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time info, public holidays</a>
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contains information on local time, sunrise and sunset,
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and public holidays in several hundred cities around the world.</li>
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<li><a href="http://www.worldtimeserver.com/">World Time Server</a>
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is another time zone database.</li>
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<li><a href="http://tycho.usno.navy.mil/tzones.html">World Time Zones</a>
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contains data from the Time Service Department of the US Naval Observatory
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(USNO), used as the source
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for the <code>usno*</code> files in the <code>tz</code> distribution.</li>
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<li><a href="http://www.airportcitycodes.com/aaa/">Airlines, Airplanes
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and Airports</a> lists current standard times for thousands of
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airports around the world. This seems to be derived from
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the <a href="http://www.iata.org/sked/publications/">Standard
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Schedules Information Manual (SSIM)</a> of the
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the <a href="http://www.iata.org/">International Air Transport
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Association</a>,
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which gives current time zone rules for
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all the airports served by commercial aviation.</li>
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</ul>
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<h2>Maps</h2>
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<ul>
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<li>The <a href="http://www.odci.gov/">United States Central
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Intelligence Agency (CIA)</a> publishes a <a
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href="http://www.odci.gov/cia/publications/factbook/reference_maps/pdf/time_zones.pdf">time
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zone map</a>; the
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<a
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href="http://www.lib.utexas.edu/maps/world.html">Perry-Castañeda
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Library Map Collection</a>
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of the University of Texas at Austin has copies of
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recent editions.
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The pictorial quality is good,
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but the maps do not indicate summer time,
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and parts of the data are a few years out of date.</li>
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<li><a href="http://worldtimezone.com/">World timezones map with
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current time</a>
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has several fancy time zone maps; it covers Russia particularly well.
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The maps' pictorial quality is not quite as good as the CIA's
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but the maps are more up to date.</li>
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</ul>
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<h2>Time zone boundaries</h2>
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<ul>
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<li><a href="http://home-4.tiscali.nl/~t876506/Multizones.html">Time
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zone boundaries for multizone countries</a> summarizes legal
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boundaries between time zones within countries.</li>
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<li>Manifold.net's <a
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href="http://www.manifold.net/download/freemaps.html">Free Maps and
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GIS Data</a> includes a Manifold-format map of world time zone
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boundaries distributed under the GPL. The GeoCommunity's <a
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href="http://software.geocomm.com/data/intl_timezones.html">International
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Time Zones</a> publishes the same data in other formats.</li>
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<li>The US Geological Survey's National Atlas of the United States
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publishes the <a href="http://www.nationalatlas.gov/timeznm.html">Time
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Zones of the United States</a> in the public domain.</li>
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<li>The GeoCommunity lists several commercial sources for <a
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href="http://spatialnews.geocomm.com/features/timezones/">International
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Time Zones and Time Zone Data</a>.</li>
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</ul>
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<h2>Civil time concepts and history</h2>
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<ul>
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<li><a href="http://physics.nist.gov/time">A Walk through Time</a>
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surveys the evolution of timekeeping.</li>
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<li><a href="http://webexhibits.org/daylightsaving/">About Daylight
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Saving Time - History, rationale, laws and dates</a>
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is an overall history of DST.</li>
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<li><a href="http://toi.iriti.cnr.it/">The
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Time of Internet</a>
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describes time zones and daylight saving time,
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with diagrams.
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The time zone map is out of date, however.</li>
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<li><a href="http://www.phys.uu.nl/~vgent/idl/idl.htm">A History of
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the International Date Line</a> tells the story of the most important
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time zone boundary.</li>
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<li><a href="http://www.statoids.com/tconcept.html">Basic Time
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Zone Concepts</a> discusses terminological issues behind time zones.</li>
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</ul>
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<h2>National histories of legal time</h2>
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<dl>
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<dt>Australia</dt>
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<dd>The Community Relations Division of the New South Wales (NSW)
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Attorney General's Department maintains a <a
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href="http://www.lawlink.nsw.gov.au/crd.nsf/pages/time2">history of
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daylight saving in NSW</a>.</dd>
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<dt>Austria</dt>
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<dd>The Federal Office of Metrology and Surveying publishes a
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table of <a href="http://www.metrologie.at/pdf/sommerzeit.pdf"
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hreflang="de">daylight saving time in Austria (in German)</a>.</dd>
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<dt>Belgium</dt>
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<dd>The Royal Observatory of Belgium maintains a table of <a
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href="http://www.astro.oma.be/GENERAL/INFO/nli001a.html"
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hreflang="nl">time in Belgium (in Dutch)</a>.</dd>
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<dt>Brazil</dt>
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<dd>The Time Service Department of the National Observatory
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records <a href="http://pcdsh01.on.br/DecHV.html"
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hreflang="pt-BR">Brazil's daylight saving time decrees (in
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Portuguese)</a>.</dd>
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<dt>Canada</dt>
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<dd>The Institute for National Measurement Standards publishes current
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and some older information about <a
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href="http://inms-ienm.nrc-cnrc.gc.ca/time_services/daylight_savings_e.html">Time
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Zones and Daylight Saving Time</a>.</dd>
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<dt>Chile</dt>
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<dd>WebExhibits publishes a <a
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href="http://webexhibits.org/daylightsaving/chile.html"
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hreflang="es">history of official time (in Spanish)</a> originally
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written by the Chilean Hydrographic and Oceanographic Service.</dd>
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<dt>Germany</dt>
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<dd>The National Institute for Science and Technology maintains the <a
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href="http://www.ptb.de/en/org/4/44/441/dars_e.htm">Realisation of
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Legal Time in Germany</a>.</dd>
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<dt>Israel</dt>
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<dd>The Interior Ministry periodically issues <a
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href="ftp://ftp.cs.huji.ac.il/pub/tz/announcements/"
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hreflang="he">announcements (in Hebrew)</a>.</dd>
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<dt>Mexico</dt>
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<dd>The Investigation and Analysis Service of the Mexican Library of
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Congress has published a <a
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href="http://www.cddhcu.gob.mx/bibliot/publica/inveyana/polisoc/horver/"
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hreflang="es">history of Mexican local time (in Spanish)</a>.</dd>
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<dt>Malaysia</dt>
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<dd>See Singapore below.</dd>
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<dt>Netherlands</dt>
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<dd><a href="http://www.phys.uu.nl/~vgent/wettijd/wettijd.htm"
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hreflang="nl">Legal time in the Netherlands (in Dutch)</a>
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covers the history of local time in the Netherlands from ancient times.</dd>
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<dt>New Zealand</dt>
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<dd>The Department of Internal Affairs maintains a brief history <a
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href="http://www.dia.govt.nz/diawebsite.nsf/wpg_URL/Resource-material-Information-We-Provide-About-Daylight-Saving">about
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daylight saving</a>. The privately-maintained <a
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href="http://www.astrologyhouse.co.nz/timechanges.htm">Time Changes in
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New Zealand</a> has more details.</dd>
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<dt>Singapore</dt>
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<dd><a
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href="http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html">Why
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is Singapore in the "Wrong" Time Zone?</a> details the
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history of legal time in Singapore and Malaysia.</dd>
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<dt>United Kingdom</dt>
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<dd><a
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href="http://www.srcf.ucam.org/~jsm28/british-time/">History of
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legal time in Britain</a> discusses in detail the country
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with perhaps the best-documented history of clock adjustments.
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The National Physical Laboratory also maintains an <a
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href="http://www.npl.co.uk/time/summer_time_archive.html">archive
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of summer time dates</a>.</dd>
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</dl>
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<h2>Precision timekeeping</h2>
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<ul>
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<li><a
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href="http://literature.agilent.com/litwebbin/purl.cgi?org_id=tmo&pub_id=5965-7984E">The
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Science of Timekeeping</a> is a thorough introduction
|
|
to the theory and practice of precision timekeeping.</li>
|
|
<li><a href="http://www.ntp.org/">NTP: The Network Time Protocol</a>
|
|
discusses how to synchronize clocks of
|
|
Internet hosts.</li>
|
|
<li><a href="http://gauss.gge.unb.ca/GMT.UT.and.the.RGO.txt"
|
|
charset="macintosh">A
|
|
Few Facts Concerning GMT, UT, and the RGO</a>
|
|
answers questions like "What is the difference between GMT and UTC?"</li>
|
|
<li><a
|
|
href="http://www.gb.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical
|
|
Times</a> explains more abstruse astronomical time scales like TT, TCG,
|
|
and TDB.</li>
|
|
<li>The <a href="http://www.iau.org/">IAU</a>'s <a
|
|
href="http://www.iau-sofa.rl.ac.uk/">Standards Of Fundamental
|
|
Astronomy</a> (SOFA) initiative publishes Fortran code for converting
|
|
among time scales like TAI, TDB, TT and UTC.</li>
|
|
<li><a href="http://www.jpl.nasa.gov/basics/bsf2-3.htm">Basics of
|
|
Space Flight - Reference Systems - Time Conventions</a>
|
|
briefly explains interplanetary space flight timekeeping.</li>
|
|
<li><a
|
|
href="http://www.giss.nasa.gov/tools/mars24/help/notes.html">Technical
|
|
Notes on Mars Solar Time as Adopted by the Mars24 Sunclock</a> briefly
|
|
describes Mars Coordinated Time (MTC) and the diverse local time
|
|
scales used by each landed mission on Mars.</li>
|
|
<li><a
|
|
href="http://hpiers.obspm.fr/eop-pc/products/bulletins/bulletins.html">Bulletins
|
|
maintained by the IERS EOP (PC)</a> contains official publications of
|
|
the Earth Orientation Parameters Product Center of the
|
|
International Earth Rotation Service, the committee that decides
|
|
when leap seconds occur.</li>
|
|
<li>The <a
|
|
href="http://www.mail-archive.com/leapsecs@rom.usno.navy.mil/">Leap
|
|
Second Discussion List</a> covers McCarthy and Klepczynski's proposal
|
|
to discontinue leap seconds, published in <a
|
|
href="http://www.gpsworld.com/">GPS World</a> <strong>10</strong>, 11
|
|
(1999-11), 50–57 and discussed further in R. A. Nelson et al.,
|
|
<a href="http://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The
|
|
leap second: its history and possible future</a>,
|
|
<a href="http://www.bipm.fr/metrologia/metrologia.html">Metrologia</a>
|
|
<strong>38</strong> (2001), 509–529.
|
|
<a href="http://www.ucolick.org/~sla/leapsecs/onlinebib.html">The
|
|
Future of Leap Seconds</a> catalogs information about this
|
|
contentious issue.</li>
|
|
</ul>
|
|
<h2>Time notation</h2>
|
|
<ul>
|
|
<li>
|
|
<a href="http://www.cl.cam.ac.uk/~mgk25/iso-time.html">A Summary of
|
|
the International Standard Date and Time Notation</a> is a good
|
|
summary of ISO
|
|
8601:1988 - Data elements and interchange formats - Information interchange
|
|
- Representation of dates and times (which has been superseded by
|
|
<a href="http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=26780">ISO 8601:2000</a>).</li>
|
|
<li>
|
|
Section 3.3 of <a
|
|
href="ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt">Internet RFC 2822</a>
|
|
specifies the time notation used in email and <a
|
|
href="ftp://ftp.rfc-editor.org/in-notes/rfc2616.txt">HTTP</a> headers.</li>
|
|
<li>
|
|
<a href="ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt">Internet RFC
|
|
3339</a> specifies an ISO 8601 profile for use in new Internet
|
|
protocols.</li>
|
|
<li>
|
|
<a href="http://www.exit109.com/~ghealton/y2k/yrexamples.html">The
|
|
Best of Dates, the Worst of Dates</a> covers many problems encountered
|
|
by software developers when handling dates and time stamps.</li>
|
|
<li>
|
|
Alphabetic time zone abbreviations should not be used as unique
|
|
identifiers for UTC offsets as they are ambiguous in practice. For
|
|
example, "EST" denotes 5 hours behind UTC in English-speaking North
|
|
America, but it denotes 10 or 11 hours ahead of UTC in Australia;
|
|
and French-speaking North Americans prefer "HNE" to "EST". For
|
|
compatibility with <a href="http://www.pasc.org/#POSIX">POSIX</a> the
|
|
<code>tz</code> database contains English abbreviations for all time
|
|
stamps but in many cases these are merely inventions of the database
|
|
maintainers.</li>
|
|
</ul>
|
|
<h2>Related indexes</h2>
|
|
<ul>
|
|
<li><a href="tz-art.htm">Time and the Arts</a></li>
|
|
<li><a href="http://dmoz.org/Reference/Time/">Open Directory -
|
|
Reference: Time</a></li>
|
|
<li><a href="http://directory.google.com/Top/Reference/Time/">Google Directory - Reference > Time</a></li>
|
|
<li><a href="http://dir.yahoo.com/Science/Measurements_and_Units/Time/">Yahoo! Science > Measurements and Units > Time</a></li>
|
|
</ul>
|
|
</body>
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</html>
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