Despite what the recommendations might say, I think the TA(k) reported in the
Circular T are not efforts by lab K to realize TAI. They are probably
unsteered timescales generated by the labs for their internal use. The values
for USNO and NIST are extremely large, for example. That whole section of the
Circular T could be just a vestigial contribution from a bygone era. Those
who needed to interface with civil time used UTC, and it seems those who needed
a continuous timescale did whatever seemed easiest at the time.
From: Michael Deckers via LEAPSECS <[email protected]>
To: Leap Second Discussion List <[email protected]>
Sent: Wednesday, November 5, 2014 3:59 PM
Subject: Re: [LEAPSECS] the big artillery
On 2014-11-05 16:27, Zefram wrote:
> ....................................................... UTC is always
> an integral number of seconds offset from TAI, and so by construction
> UTC(NPL) is always an integral number of seconds offset from TAI(NPL).
> Hence each of the marks also occurs at the top of a second of TAI(NPL).
The symbol TAI(k) is defined in
RECOMMENDATION ITU-R TF.536-2: Time-scale notations
of 2003 with the text:
TAI(k): Time-scale realized by the institute “k” and defined
by the relation TAI(k) = UTC(k) + DTAI, where DTAI
is the number of integral seconds specified by the
International Earth Rotation Service (IERS) as
being the difference between UTC and TAI;
I do not know whether that notation has ever been put
to serious use outside this recommendation.
The contributions by the various metrology institutes to TAI
are independent from the UTC(k) and are denoted by TA(k) in
Circular T by the BIPM. The recommendation explains it as:
TA(k): Atomic Time-scale, as realized by the institute “k”;
Michael Deckers.
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