Poul-Henning Kamp wrote on 2006-01-19 17:56 UTC:
> >For TAI I'd suggest 1958-01-01, when TAI and UT were set nearly together.
>
> I chose the time when TAI became constant rate so that
> all the rubber seconds are confined to negative values.
Please remember that the TAI second differed noticeably from the SI
second until about 1998, because black-body radiation shift was not
taken into account in the definition of TAI before then. Also caesium
fountains have improved quite a lot shortly before 2000.
Therefore, if people ask me for my favourite epoch for a new time scale,
then it is
2000-03-01 00:00:00 (preferably UTC, but I would not mind much
if it were TAI, or even "GPS time")
This epoch has the following advantages:
a) It is well after TAI rubber seconds were fixed in ~1998,
so we know the time of *that* epoch with much greater accuracy than
any before 1998.
b) It is a date that very slightly simplifies calendrical calculation,
because it is located at the end of a leap day and at the end of
a Gregorian mod 400 years cycle. (Otherwise, you would have to shift
to that date each time to convert scalar <-> YYYY-MM-DD notation.)
c) It is a date sufficiently recent, such that implementors will be forced to
properly test their handling of pre-epoch arithmetic, something
easily neglected in practice with epochs before 1980.
Markus
--
Markus Kuhn, Computer Laboratory, University of Cambridge
http://www.cl.cam.ac.uk/~mgk25/ || CB3 0FD, Great Britain
Received on Thu Jan 19 2006 - 11:01:06 PST