Subject: Re: Representing Time
From: (Rob Warnock)
Date: 1999/03/18
Newsgroups: comp.lang.lisp
Message-ID: <7cpuju$>
Kent M Pitman  <> wrote:
| Leap seconds are what bother me the most.  The fact that politically
| an organizational body can insert an extra second between two times
| means that any representation of a future time is virtually, not
| actually, correlated to the calendar.

Are you sure you're not talking about Daylight Savings Time instead of
leap seconds?  Except for the one discontinuity in 1972 when everyone
switched to UTC (Coordinated Universal Time) -- which *did* require
"political" agreement among a bunch of nations -- leap seconds are only
added as needed to keep "noon" within a second of noon, especially when
*non*-periodic (and therefore unpredictable by direct extrapolation *or*
political bodies!) variations in the rotation in the Earth occur. And
they're only added (or removed, but so far none have been) at midnight
December 31st or June 30th, so a fairly small vector of (4 bits/year
since 1972) can be used to adjust.

Note: I'm not sure how far in the future they can reliably predict when
leap seconds will have to be inserted. Maybe the following URLs will help:

Looking at this last one, it's pretty clear that the insertion rate of
leap seconds is *not* a simple periodic function...


Rob Warnock, 8L-855
Applied Networking
Silicon Graphics, Inc.		Phone: 650-933-1673
2011 N. Shoreline Blvd.		FAX: 650-964-0811
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