[time-nuts] The TAI zero epoch of 1958

[Scott Stuart]

Hello!  I'm new to the list and I have a question about time systems.

The context is that someone is going to be communicating timestamps to me
in TAI formatted as the number of elapsed seconds since 1958 Jan 1
00:00:00.  To make sure that I understand how this is being calculated, I
reviewed the history of the establishment of TAI and UTC in the late 60s
and early 70s.  I understand why 1972 Jan 1 00:00:00 UTC == 1972 Jan 1
00:00:10 TAI and why TAI is now 37 seconds ahead of UTC.  I can also see
that propagating backwards from the 1961 time conversion formulas to 1958
Jan 1 gives TAI - UTC very close to 0 (within about 2 milliseconds).  So,
it makes sense to use 1958 Jan 1 00:00:00 UTC == 1958 Jan 1 00:00:00 TAI as
the 0 epoch for TAI in seconds.

But, I also came across this statement:

*Loran-C*, Long Range Navigation time, is an atomic time scale implemented
by the atomic clocks in Loran-C chain transmitter sites. Loran time was
zero at 0h 1-Jan-1958 and since it is not perturbed by leap seconds it is
now ahead of UTC by 27 seconds.

Loran-C time seems to be currently ticking synchronously with TAI but is 10
seconds behind TAI.  Does that mean that when TAI and UTC were
defined/synchronized in 1972, that the extra 10 seconds were not added to
Loran time?  And that the statement above should be that 1958 Jan 1
00:00:00 UTC == 1957 Dec 31 23:59:50 Loran?

Thanks,
  Scott


-- 
"Of what avail are forty freedoms without a blank spot on the map? "
— Aldo Leopold