[time-nuts] What time is it anyway?

[Arnold Tibus]

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/
>>