Re: Upgrade, don't degrade

From: Paul Eggert <>
Date: Tue, 8 May 2001 15:07:35 -0700 (PDT)

   From: Ken Pizzini <ken_at_HALCYON.COM>
   Date: Mon, 9 Apr 2001 21:20:06 -0700

   I will sheepishly admit that I am ignorant of the details of the
   problem(s) that leap seconds were designed to fix; I look forward
   to reading a good technical history of how UTC came to be.

I looked for such a history, and couldn't find one on the web.
However, I did find the following tidbits:

* |UT1-UTC| must have been smaller during the period 1961-1972 than
  it has been since then; this is because UTC ticks were a bit longer
  than TAI ticks back then, so UTC could keep closer to UT1.
  (See <>.)

* The tolerance for |UT1-UTC| was loosened in 1975.
  Between 1972 and 1975 it was 0.7 s; since then, it has been 0.9 s.
  (See <>.)
  The newer, looser standard has been required on three occasions
  since 1975, most recently after the last leap second in December 1998.

So, from the point of view of minimizing |UT1-UTC|, we degraded twice
in the past 30 years: once in 1972 when the current leap second regime
was introduced, and once in 1975 when the maximum value of |UT1-UTC|
was increased.

There must have been some debate and discussion when these changes
occurred. Does anybody on this list know what the debate was about?
Before proposing a major new change, it would be helpful to know why
the previous major change was made, and how successfully the change
accomplished its goals.

PS. I did find an abstract to Chadsey and McCarthy's paper "Relating
time to the earth's variable rotation", presented at last year's PTTI
meeting. From its abstract, it sounds like this paper is be relevant
and might help further the discussion. I assume this paper is a
government publication; can it be made available on the net? Here's
the abstract:
Received on Tue May 08 2001 - 15:17:54 PDT

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