[ntp:questions] National time standard differences

Mabry Tyson Tyson at AI.SRI.COM
Thu Feb 11 20:23:56 UTC 2010

On 2/11/10 11:45 AM, Richard B. Gilbert wrote:
> unruh wrote:
>>>> Since the flight probably lasted say 10 hr, which is 100000 sec, th
>>>> eclocks would have been out by about 1usec. Assuming that the clocks
>>>> could then have been synchronized, that would mean that US and
>>>> Switzerland time have been out by about 1usec. (Why they would fly 
>>>> from
>>>> Palo Alto when the time standard is in Washington DC I have no idea).
>>> Probably because the clocks came out of the HP Palo Alto office?
>> But if they are comparing time standards, it does not matter where the
>> clocks were manufactured, but where they are synchronized with the time
>> standard, and that is surely in Washington, not Palo Alto. You do not 
>> try to synchronize a clock in Washington via phone lines or
>> microwave links with Palo Alto surely.
> ISTR that NIST has facilities in both Colorado and Hawaii.  The 
> Washington DC area has the U.S. Naval Observatory.
People might want to look at articles at
(A fun site!  )

The 1965 "Cesium Beam ..." article:
> In June 1964, two commercial cesium standards which
> had been taken to Switzerland for an instrument
> exhibition were compared with the long cesium
> standard at LSRH in Neuchatel (BAGLEY and CUTLER,
> 1964). Four days later the commercial instruments
> were measured in terms of the NBS standard in
> Boulder, Colorado, after being kept in continuous
> operation during the intervening time. The results of
> these measurements again showed the Swiss and U. S.
> standards to be in agreement to better than 1 X 10-11.
> The assumption of perfect stability of the commercial
> standards between comparisons did not appear to
> timit the measurements in view of the excellent longterm
> stability demonstrated by these instruments
> during one week's continuous operation in Switzerland.
and at the end of the article:
> ... Clocks
> based on these time scales have been synchronized over
> intercontinental- distances by clock-carrying experiments,
> use of radio transmissions, and use of artificial earth satellites.
> Accuracies of the order of 1 microsecond have been achieved.
The site also lists a 1978 article and notes "This is the earliest 
reference I've found to the relativistic corrections needed for GPS."

Ah.. you can read all about the experiment in

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