[LEAPSECS] the big artillery

[Warner Losh]

On Nov 5, 2014, at 7:57 PM, Alex Currant via LEAPSECS <leapsecs at leapsecond.com> wrote:

> 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, since it is hard to imagine how a lab could get a different offset attempting to realize TAI from attempting to realize UTC. The values for USNO and NIST are extremely large, for example  The TA(k) are probably unsteered timescales generated by the labs for their internal use.

That’s definitely the case. They are their own internal time scales that are usually not steered. Steering introduces complication into knowing what to do with the error terms, so most of the time systems I’ve seen usually have an un-steered component that is measured against the signal that you want to generate to steer that signal. TA(k) isn’t implied to be TAI anything anywhere in the recommendations that I could see.

Warner

> On the other hand, maybe that whole section of the Circular T is 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.   Today, those who need a continuous timescale to interface with civil time, or who don't know what they are doing, can always be pleasantly surprised by a chance to earn overtime at New Year's or on July 1.
>  
> 
> 
> 
> 
> From: Michael Deckers via LEAPSECS <leapsecs at leapsecond.com>
> To: Leap Second Discussion List <leapsecs at leapsecond.com> 
> 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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