[time-nuts] What time is it anyway?

Steve Rooke sar10538 at gmail.com
Sun Mar 28 12:06:17 UTC 2010


And all this goes to prove is that:
A man with one clock knows what time it is;
A man with two clocks is never quite sure.
:)

On 29 March 2010 00:58, Arnold Tibus <Arnold.Tibus at gmx.de> wrote:
> The answer looks to me a bit difficult reading the USNO definition :
>
> INTERNATIONAL TIME SCALES AND THE B.I.P.M.
> http://tycho.usno.navy.mil/bipm.html
>
> citing:
> "...the U.S. Naval Observatory timescale, UTC(USNO),
> and its real-time implementation,  Master Clock #2  (MC #2),
> are kept within a close but unspecified tolerance of the
>  international atomic timescale published
> by the  Bureau International des Poids et Mesures
> (International Bureau of Weights and Measures [BIPM])
>  in Sevres, France."
>
> "...Hence, all these atomic timescales are called
> Coordinated Universal Time (UTC), of which USNO's
> version is UTC(USNO)."
>
> "...The difference between UTC (computed by BIPM) and any other
> timing center's UTC only becomes known after computation and
> dissemination of UTC, which occurs about two weeks after the fact.
> This difference is presently limited mainly by the long-term frequency
>  instability of UTC.
> UTC(USNO) has been kept within 26 nanoseconds of UTC during
> the past year through frequency steering of our Master Clocks to our
> extrapolation of UTC."
>
> So I do understand that BIPM is the world's time keeper, but there
> may be a difference between the UTCs  of up to 26ns?
>
> "...Since synchronization is never perfect, we provide the latest data
> below on the differences between UTC and the UTC of other timing
> centers, including USNO,..."
> and
> "...All of our reference clocks are real-time approximations of UTC(USNO),
>  and as such are denoted UTC(USNO,MC). Master Clock #2 (MC #2) is
> our official reference clock..."
>
> So I understand this as, that the USA do refer to the time reference
> of USNO - and the rest of the world to BIPM directly?
>
> Since dec. 2009  the PTB in Braunschweig, Germany (with the new
> CSF2) and the BIPM in Sevre are the only countries running 4 of the
>  most precise primary Cs fountain clocks, if I am informed correctly.
> Together they should run quite close to the time defined by BIPM I think,
> and according our law our official time is transmitted by the PTB.
>
> Now, How do I have to interprete the readout of GPSDOs like
> Trimble's Thunderbolt and others PPS difference in ns to UTC?
>
> To which UTC? I suppose to the time transmitted by the US GPS SATs.
> Is there another difference in UTC to BIPM included?
> What is with Glonass (and will be later perhaps with Galileo)?
>
> In fact the use of GPS is already spreaded all over the world and
> in use in many technical applications, meaning that the world does
> refer to UTC given by US GPS !?
>
> Does it make sense under this circumstance as Time Nut to go
> below the Xns (26ns ?) frontier as absolute measure?
> Will this ever be possible? (Everything is relative...)
>
> But excuse me in case I do miss and misunderstand something
> fully...
>
> Arnold, DK2WT
>
>
> On Sun, 28 Mar 2010 22:29:22 +1300, Steve Rooke wrote:
>
>>What puzzles me is who is the keeper of "legal time" for the other
>>93.4% of land mass and 95.5% of population of the World other than the
>>US.
>
>>On 28 March 2010 04:49, David Forbes <dforbes at dakotacom.net> wrote:
>>> At 11:11 AM -0400 3/27/10, Bob Camp wrote:
>>>>
>>>> I would bet that if you went deep enough into the details, that the Army
>>>> at some point was less than enthusiastic about having to ask the Navy when
>>>> ever they wanted to know what time it was.
>>>
>>> My guess is that the Army just asked Western Union, who asked the Navy.
>>>
>>> --
>>>
>>> --David Forbes, Tucson, AZ
>>> http://www.cathodecorner.com/
>>>
>
>
>
>
>
>
>
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-- 
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.



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