[time-nuts] Primary Time Standards
Bob Camp
lists at rtty.us
Thu Jul 14 16:56:29 UTC 2011
Hi
One would assume that mean sea level / 1 G would be the standard reference
point for the "official" Cs transition. I've never seen anybody pull out a
gravity meter to set up their Cs though. I suspect that NIST has at least
done the math.
Bob
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Mike S
Sent: Thursday, July 14, 2011 6:26 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Primary Time Standards
At 10:26 PM 7/13/2011, Jim Palfreyman wrote...
>But why is it that Caesium Clocks and Hydrogen Masers have an
>adjustment
>facility?
Cs defines the second, but only at the physically impossible
temperature of absolute zero. Relativistic effects make it so the
second is a different length at different altitudes.
So, when one wants to track global "mean" time, individual clocks need
adjustment.
Which brings up another question - what altitude (=geoid?) is TAI
defined for? I don't know enough about general relativity, but think
the latitude would make a difference, too?
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