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.
Ed.
