On 2011 Feb 2, at 23:44, Tom Van Baak wrote:
> Over the past 4 decades the recommended tolerance for
> DUT1 has gone from 0.1 s to 0.5 to 0.7 to 0.9 seconds.
The 0.7 was in the original 1970 version of Rec. 460 which was
supposed to let DUT1 fit in 3 bits of BCD clicks. The
response from the BIH must have been something like "The earth
is spinning slower now than it has since 1912 and we have to
compute this stuff by hand using input data that's delivered
to us by boats so we can't give you better than 0.9 s", and
that's what was written into the first revision of Rec. 460.
Fortunately for everyone the earth's crust speeded up starting
right then, so 1972 was the only year with two leap seconds.
However, this suggestion of increasing the limit of DUT1 should
go hand in hand with another change made in Rec. 460. The original
draft of 460 which was presented to the CCIR Plenary Assembly
suggested that the leaps should be full seconds or "integral
multiples thereof".
Somehow during the discussions at the Plenary Assembly the phrase
in quotes was deleted before adoption of the draft recommendation.
(I hope that the delegates to the Radiocommunications Assembly
which votes on the current draft revision of TF.460 feel equally
empowered to change the wording.) Anyway, if the limit on DUT1 is
increased thus then it might make sense to re-instate the mythical
POSIX "double leap second".
--
Steve Allen <[email protected]> WGS-84 (GPS)
UCO/Lick Observatory Natural Sciences II, Room 165 Lat +36.99855
University of California Voice: +1 831 459 3046 Lng -122.06015
Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
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