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From: wcwells%ucbopal.CC@Berkeley.ARPA
Newsgroups: net.mail.headers
Subject: Re:  Several questions/comments on time zones
Message-ID: <8401290501.AA03216@ucbopal.CC.Berkeley.ARPA>
Date: Sat, 4-Feb-84 00:01:58 EST
Article-I.D.: ucbopal.8401290501.AA03216
Posted: Sat Feb  4 00:01:58 1984
Date-Received: Sun, 5-Feb-84 04:14:45 EST
Sender: ka@hou3c.UUCP (Kenneth Almquist)
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To: Header-People@MIT-MC, v.wales@UCLA-LOCUS

On zero time zone designators:

In addition to UT, UTC, Z, and GMT, I have also heard of GCT
(C for Civil).

Z ("Zulu" or "Zero" time zone) is the military term. As far as US Armed
Forces is concerned, it is the time transmitted by the Dept. of
Commerce radios stations WWV and WWVH (hope I got the call signs
correct). WWV previously transmitted GMT time, but since the early/mid
70's has been transmitting Coordinated Universal Time(UTC). Perhaps
someone can give us some history of the name change. GMT, GCT, PST/PDT,
etc.  are local Civil time designators. UT and UTC maybe defined by
international treaty/agreement (anybody know?).

I also suspect that UTC is not the same as GMT (seconds apart?).

Does any one have the name of time used by the "star gazers"?

On date/time stamping of message:

Things would be a lot easier if messages on the network would be dated
and time stamped with UTC (or "Z") time. If you want local time and
date presented/used by your users, convert the time and date in your
presentation (user interface) program(s). The military, and I think,
most international communications companies use only one time zone to
identify messages.  Why can't we?

On converting UTC to/from local time:

	01:00:01 01 Jan 84 UTC	is	17:00:01 31 Dec 83 PST

Note the day and year difference. When converting local time to UTC,
the day and year must be converted as well.  It's not hard to do. For
PST, the rule is to add 8 hours to the current time (since the sun
comes up 8 hours earlier in England than it does on the U.S. West
Coast). If the resulting hour is greater that 24, subtract 24 hours
from the hours and add 01 to the day (and add 1 to the year if the
original day is 31 Dec).  (For PDT add 7 instead of 8 hours to get
UTC). I will let you figure out how to convert the other way.

New subject: When does the day change?

Or is 00:00:00 today, really 24:00:00 yesterday?
I think the military avoids the issue by never using 00:00 or 24:00
(hours and minutes) to identify messages.

Bill Wells
wcwells@Berkeley.ARPA