[LEAPSECS] Time math libraries, UTC to TAI

[Steve Allen]

On Wed 2016-12-28T16:00:17 -0500, Brooks Harris hath writ:
> I don't think so. This is POSIX so-called "1970-01-01 00:00:00 UTC"
> not 1588/PTP. 1588/PTP epoch is 10s earlier.

At 1970-01-01 the difference TAI - UTC(BIH) was 8.000082 SI seconds.

The first version of IEEE 1588 was not entirely consistent with its
text and appendix information, so it was not clear whether that time
scale was supposed to be TAI or TAI - 10.
The second version of IEEE 1588 clarified that the intent is TAI.

The choice of TAI - 10 would put the origin of the time scale at the
intersection of the grey vertical line and the green horizontal line
seen in the second plot on
http://www.ucolick.org/~sla/leapsecs/amsci.html
And for any system using that time scale that puts the origin at
1.999918 SI seconds after the (BIH average of the) radio broadcast
time signals said it was 1970-01-01T00:00:00.

But all of this is pedantic and moot for any currently operational
system because it was not operational then.  Only a few things like
astrometry of solar system bodies and spindown of a handful of pulsars
have data and models with enough precision to discern this.

Everything and everyone else can reasonably assert that they do not
have to care and that every day has always had 86400 seconds of
duration equal to what they are currently ticking.

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