Re: [LEAPSECS] Introduction of long term scheduling

From: Ed Davies <ls_at_EDAVIES.NILDRAM.CO.UK>
Date: Tue, 02 Jan 2007 18:36:45 +0000

Steve Allen wrote:
> On Mon 2007-01-01T21:19:04 +0000, Ed Davies hath writ:
>> Why does the "One sec at predicted intervals" line suddenly
>> diverge in the early 2500's when the other lines seem to just
>> be expanding in a sensible way?
> ...
> I suspect that the divergence of the one line indicates that the LOD
> has become long enough that 1 s can no longer keep up with the
> divergence using whatever predicted interval he chose. I suspect that
> the chosen interval was every three months, for it is in about the
> year 2500 that the LOD will require 4 leap seconds per year.

Yes, that make sense. I worked out what LOD increases he'd have
to be assuming for one or 6 monthly leaps and neither seemed right.
Should have realised that it was in between.

Still, it's a strange assumption, given that TF.640 allows, I
understand, leaps at the end of any month. Unofficially, the
wording seems to be:

> A positive or negative leap-second should be the last second
> of a UTC month, but first preference should be given to the end
> of December and June, and second preference to the end of March
> and September.

Anybody got access to a proper copy and can say whether that's
right or not? If it is right then the Wikipedia article on leap
seconds needs fixing.

> As for the other questions, McCarthy had been producing versions of this
> plot since around 1999, but the published record of them is largely
> in PowerPoint. Dr. Tufte has provided postmortems of both Challenger
> and Columbia as testaments to how little that medium conveys.

Indeed, this slide hasn't got us much closer to understanding the
original problem, namely: what is maximum error likely to be over
a decade.

Received on Tue Jan 02 2007 - 10:37:21 PST

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