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diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node107.html b/sag-0.6.1-www/Invisible/sag-0.6/node107.html new file mode 100644 index 0000000..22006ec --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node107.html @@ -0,0 +1,87 @@ +<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> +<!--Converted with LaTeX2HTML 96.1-h (September 30, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --> +<HTML> +<HEAD> +<TITLE>Time zones</TITLE> +<META NAME="description" CONTENT="Time zones"> +<META NAME="keywords" CONTENT="sag"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<LINK REL=STYLESHEET HREF="sag.css"> +</HEAD> +<BODY LANG="EN" > + <A NAME="tex2html1663" HREF="node108.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html1661" HREF="node106.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html1655" HREF="node106.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html1665" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html1666" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html1664" HREF="node108.html">The hardware and software </A> +<B>Up:</B> <A NAME="tex2html1662" HREF="node106.html">Keeping Time</A> +<B> Previous:</B> <A NAME="tex2html1656" HREF="node106.html">Keeping Time</A> +<BR> <P> +<H1><A NAME="SECTION001210000000000000000">Time zones</A></H1> +<P> + Time measurement is based on mostly regular natural + phenomena, such as alternating light and dark periods + caused by the rotation of the planet. The total time + taken by two successive periods is constant, but the + lengths of the light and dark period vary. One simple + constant is noon. +<P> + Noon is the time of the day when the Sun is at its highest + position. Since the Earth is round,<A NAME="tex2html53" HREF="footnode.html#3113"><IMG ALIGN=BOTTOM ALT="gif" SRC="./foot_motif.gif"></A> noon happens at different times in + different places. This leads to the concept of <b>local + time</b>. Humans measure time in many units, most of which are + tied to natural phenomena like noon. As long as you stay in + the same place, it doesn't matter that local times differ. +<P> + As soon as you need to communicate with distant places, you'll + notice the need for a common time. In modern times, most of + the places in the world communicate with most other places in + the world, so a global standard for measuring time has been defined. + This time is called <b>universal time</b> (UT or UTC, formerly + known as Greenwich Mean Time or GMT, since it used to be local + time in Greenwich, England). When people with different local + times need to communicate, they can express times in universal + time, so that there is no confusion about when things should happen. +<P> + Each local time is called a time zone. While geography would + allow all places that have noon at the same time + have the same time zone, + politics makes it difficult. For various reasons, many countries + use <b>daylight savings time</b>, that is, they move their + clocks to have more natural light while they work, and then move + the clocks back during winter. Other + countries do not do this. Those that do, do not agree + when the clocks should be moved, and they change the rules + from year to year. This makes time zone conversions definitely + non-trivial. +<P> + Time zones are best named by the location or by telling the + difference between local and universal time. In the US and + some other countries, the + local time zones have a name and a three letter abbreviation. + The abbreviations are not unique, however, and should not be + used unless the country is also named. It is better to talk + about the local time in, say, Helsinki, than about East + European time, since not all countries in Eastern Europe follow + the same rules. +<P> + Linux has a time zone package that knows about all + existing time zones, and that can easily be updated when the + rules change. All the system administrator needs to do is to + select the appropriate time zone. Also, each user can set + his own time zone--this is important since many people work + with computers in different countries over the Internet. + When the rules for daylight savings time change in your local + time zone, make sure you'll upgrade at least that part of your + Linux system. Other than setting the system time zone and + upgrading the time zone data files, there is little need to + bother about time. +<P> +<HR><A NAME="tex2html1663" HREF="node108.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html1661" HREF="node106.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html1655" HREF="node106.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html1665" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html1666" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html1664" HREF="node108.html">The hardware and software </A> +<B>Up:</B> <A NAME="tex2html1662" HREF="node106.html">Keeping Time</A> +<B> Previous:</B> <A NAME="tex2html1656" HREF="node106.html">Keeping Time</A> +<P><ADDRESS> +<I>Lars Wirzenius <BR> +Sat Nov 15 02:32:11 EET 1997</I> +</ADDRESS> +</BODY> +</HTML> |