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From: jeff@rtech.ARPA (Jeff Lichtman)
Newsgroups: net.micro.mac
Subject: Re: Date and time keeping
Message-ID: <383@rtech.ARPA>
Date: Sun, 12-May-85 01:57:52 EDT
Article-I.D.: rtech.383
Posted: Sun May 12 01:57:52 1985
Date-Received: Fri, 17-May-85 01:17:43 EDT
References: <2254@seismo.UUCP>
Organization: Relational Technology, Berkeley CA
Lines: 30

> Ah yes, the old bugaboo of keeping system time in some awful local time.
> One of the things done right by Unix is to keep system time in GMT
> (or CUT as it is now known to some degree in inaccuracy) and convert using
> an adjustable bias when displaying it to humans.  System III's predicessor
> started the useful hack of making this bias a per-user adjustable
> quantity, so if I am on the East Coast using a West Coast computer,
> "date" can give me "my local time".  So, by keeping system time in CUT,
> you don't have to adjust the clock when you get off the plane - this
> can cause havoc with things like Make - OOPS, don't have such tools
> on the Mac :-)!!!  You just adjust the offset for the local bias from GMT.
> 
> 	Temporally yours,
> 	-Mike O'Dell

This will work, but it's easy to do it wrong and paint yourself into a corner.
Some parts of the world have time zones that are not an integral number of
hours different from Greenwich.  For instance, the middle part of Australia
is 30 minutes different from its ends.  If the person who wrote the
configuration program didn't know this, he or she might be tempted to simply
have an integer parameter to stand for the number of hours difference between
Greenwich and local time.

If you ever have to write software that stores time as GMT, and you ever want
to sell it internationally, you would do well to remember this.
-- 
Jeff Lichtman at rtech (Relational Technology, Inc.)
aka Swazoo Koolak

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