[LEAPSECS] [QUAR] Bulletin C and all that

[Michael Deckers]

   On 2015-01-26 20:05, Brooks Harris wrote:

> As a practical matter of modern timekeeping the UTC timescale started at
> 1972-01-01T00:00:00Z (UTC). NTP, POSIX, 1588/PTP and others refer to epochs and
> timescales they call "UTC" that occur earlier than 1972-01-01, so this confuses
> matters. But those epochs exist on "Gregorian calendar timescale that is
> proleptic to the UTC origin", not on the modern UTC timescale proper. We've got
> to get past this confusion.

   A calendar provides a method for denoting datetime values.

   A time scale is a coordinate function within coordinate systems for
   physical (astronomical) models that assigns datetime values to each
   point in its domain of definition.

   Hence a calendar should not be confused with a time scale, even if
   the calendar is used exclusively for the notation of the values of a
   single time scale (which is not the case for the Gregorian calendar).

   Values of the time scale later called UTC by the BIH can be exactly
   related to TAI since 1961, see
       [hpiers.obspm.fr/iers/bul/bulc/UTC-TAI.history].

> Steve Allen's Time Scales page points out -
>
> Time Scales
> http://www.ucolick.org/~sla/leapsecs/timescales.html
>
> "Nothing resembling the name UTC was used prior to 1960, so any claim that UTC
> can be used before then is inappropriate. The name UTC did not appear in any
> official context until 1974, so any claim that UTC was used prior to 1974 is
> almost certainly a reinterpretation of history which does not correspond to
> anything in contemporary documents."
>
> The history is tangled, but none of it matters except to historians.

   I think that "1974" is just a typo for "1964"; I do not see any error
   in the history.

   Michael Deckers.