[time-nuts] Primary Time Standards

[Bob Camp]

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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