On 2011-01-14 16:26, Warner Losh wrote:
The BIPM collects time and frequency data for the different clocks,
measured against each other. Each clock then has an error in frequency
and time computed. These clocks are then weighted based on assigned
values (based on the time scientists best guest about how good the
clocks are). This value goes in to producing what's called a 'paper
clock' which is a historical look at what the best guess at the actual
time for each of these measurements. Based on that, you can know how
close your clocks are running, and can steer them, if you wish.
The actual process as used by the BIPM (since 1977) is a bit more
complex. The weighted mean of atomic clock readings results in an
intermediate time scale called EAL (échelle atomique libre);
in a second step, TAI is determined as an affine function of EAL
so as to approximate the frequencies of the best atomic clocks.
See for examle
Dennis D McCarthy, P Kenneth Seidelmann: "Time -- From
Earth Rotation to Atomic Physics". Wiley-VCH. 2009.
pages 201..216.
The process was even more complex while the rate of TAI was
intentionally increased during 1995..1998.
Michael Deckers.
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