[LEAPSECS] the big artillery

[michael.deckers]

    On 2014-11-03 01:58, Warner Losh wrote:

> A common grid is an artificial construct that measurements from
> different clocks can be interpolated to. The top of second (or other
> phase) measurements place place the top of second in time. Interpolating
> to a grid places the time of each time scale at a fixed point on the grid
> so they can be compared by simple subtraction. The interpolation causes
> the local measurement device’s time scale to subtract out, and gives
> phase measurements at a specific time.
>
> For example, if UTC top of second for second 1 comes in at local time scale
> 1.1 and 2.1 and the UT1 PPS for second 1 comes in at 0.95 and 1.96[*], you
> can interpolate a phase at time 1.0 on the local time scale for each of these
> clocks and know the phase difference at 1.0. Do this for 1.0, 2.0, etc and you
> can make phase and frequency statements about UTC and UT1.
>
> [*] I know this is absurdly large, it should be 1.950000001 or so)
>
> Is this required? In the general case it is, but in specific other cases it may
> not be absolutely required. It also generalizes to clocks whose frequency
> may not be 1Hz.
>
> This method also assumes that the local time scale (oscillator) is more stable than
> the acceptable error over the interpolation period, since all physical oscillators are
> imperfect.

    Thank you for the explanation! So a grid works as a kind of laboratory
    time scale to be used as a reference during measurements.

    You also replied to my statement:

>>    UT1 is a timescale that ticks 1 SI second when the Earth Rotation Angle
>>    increases by exactly (2·π rad)/86 636.546 949 141 027 072,
>
> Which it rarely does for any length of time.

     On the contrary, the fixed angular speed d(ERA)/d(UT1) is a
     defining property of UT1, and it is an "auxiliary defining
     constant" in the IAU 2009 system of constants.

     Michael Deckers.