[ntp:questions] National time standard differences
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
>>>> 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
More information about the questions