[LEAPSECS] Looking-glass, through

Michael Deckers michael.deckers at yahoo.com
Fri Jan 14 12:49:50 EST 2011

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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