[tz] What's "right"?

Steve Allen sla at ucolick.org
Sat Nov 14 02:45:22 UTC 2020

On Fri 2020-11-13T16:43:14-0800 Guy Harris hath writ:
> So what documents indicate how UTC was implemented prior to 1972-01-01 00:00:00 UTC?

The source documents for the practice are the publications of the
Bureau International de l'Heure, namely Bulletin Horaire through
1966 and Circular D after that.  See the index of issues
Within those issues are references to the international agreements
which BIH was tasked to implement, and a lot more nitty gritty.
detail than is found in wikipedia or any summary.

> And what documents discuss the changeover to "new" UTC (decision made in 1970 to start "new UTC' in 1972?)?

The source documents are from the BIH, CCDS, CIPM, CGPM, IAU, URSI,
CCIR, IEEE, etc., and also memoirs of the dramatis personae at those
meetings.  Again, no summary tries to capture the whole story, and
it is evident that details were redacted from the public proceedings.

> And, for anybody who cares in that much detail about the definition
> of the Epoch, should 1970-01-01 00:00:00 UTC be interpreted as
> *literally* being 1970-01-01 00:00:00 UTC, or as 1970-01-01 00:00:00
> "new UTC extended backwards", i.e.  "TAI, and new UTC extended
> backwards, were 10 seconds apart from the beginning of TAI all the way
> up to 1972-06-30 23:59:59, and then new UTC started getting leap
> seconded"?

If you ask me for the value of arcsin(-2) I can give you a value,
but the utility of that value requires understanding complex analysis.
The answer depends on the needs of the application.

Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
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