[time-nuts] 15 Seconds error...??

mike cook michael.cook at sfr.fr
Thu Jan 19 04:02:56 EST 2012


Le 19/01/2012 01:04, Mike S a écrit :
>
> On 1/18/2012 6:15 PM, mike cook wrote:
>> I'm not sure anyone says "don't" use TAI. What they say is that you
>> "can't" use TAI because it is not disseminated , unlike UTC(k).
>> UTC has the same rate as TAI , so we have a source of Si ticks, but TAI
>> is not on the wire.
>
> But there's the rub. Many people/organizations use "UTC," and it's 
> enshrined in many legal systems. But, just like TAI, is really only on 
> paper as it isn't known until after the fact, when all the 
> contributing clocks are compared and the data massaged.
>
> Are the after-the-fact published offsets between, say, UTC(USNO) and 
> TAI and UTC different? (except for the integer TAI/UTC difference)?

The answer is yes,  (with a resolution of nanoseconds), and the data is 
published by the BIPM. The annual report of the BIPM describes the 
process and gives links to relative publications ( see bipm.org site ).

> I guess I'm assuming that TAI is published as after-the-fact offsets 
> from clocks which are disseminated

No the free running clocks from which TAI is derived are not 
disseminated electronically , at least not officially.

> , which means UTC(k), no?

Hmmmm (from a time serf).  Some labs provide UTC(k) but do not generate 
a TA(k) , maybe as there not enough clocks available.  Some UTC(k) 
providers have only one clock,.

>
> Put another way, can someone say they know UTC any better than they 
> know TAI?

Must apply to those labs.

>
> US Code says "Coordinated Universal Time defined
> In this section, the term “Coordinated Universal Time” means the time 
> scale maintained through the General Conference of Weights and 
> Measures and interpreted or modified for the United States by the 
> Secretary of Commerce in coordination with the Secretary of the Navy."
>
> You tell me, is that UTC, or UTC(USNO) or UTC(NIST), or something 
> completely different?
>


As the time lord in the case of UTC is BIPM seconded (if I may make the 
pun) admirably by Daniel Gambis, it is UTC,  but for practical purposes 
it is either of the national labs, the "or modified by" bit being just 
an assertion of sovereignty.





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