[LEAPSECS] Looking-glass, through

[Michael Deckers]

    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.