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Re: [Gnu-arch-users] s/GMT/UTC/

From: Andrew Suffield
Subject: Re: [Gnu-arch-users] s/GMT/UTC/
Date: Tue, 7 Sep 2004 11:24:39 +0100
User-agent: Mutt/1.5.6+20040818i

On Tue, Sep 07, 2004 at 12:08:26AM -0400, Phil Frost wrote:
> GMT is not UTC at all, at least if you are concerned with accurate time.
> GMT is the observed time at the greenwich observatory, which is
> determined by astronomical observances, not atomic clocks. It is
> problematic for people who require accurate time because the earth's
> rotation is not uniform.
> UTC is determined by atomic clocks, and it is defined with a uniform
> second. Leap seconds are used to keep UTC within 1s of GMT, lest UTC
> would drift from the observed time on Earth.
> All civil time systems use UTC.

Other way around. They mostly use GMT because they have to. A few use
something strange that is neither GMT nor UTC.

UTC is only of interest to researchers. It is problematic for
everybody else because keeping it in line with the seasons makes the
conversion unpredictable.

> NTP uses UTC, as well as any time you will get from any other time
> service, radio, phone, or whatever.

This is only true from a rather skewed perspective. For example, NTP
ensures that the *current* time of your clock is correct... but the
output of:

ctime(time() + 10000000)

Will be wrong. Thusly UTC is quite impossible to use for civil
purposes. It denies you the ability to talk about times in the future.

  .''`.  ** Debian GNU/Linux ** | Andrew Suffield
 : :' : |
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