[time-nuts] Cesium vs H Maser clocks

[Neville Michie]

Someone asked what a frequency time standard cam calibrate besides a  
clock.
Gravity is, or was, measured by throwing a corner cube into the air  
(vacuum)
and using a laser interferometer, timing its acceleration as it fell  
back.
All of that can be calibrated from a frequency standard, so unlike  
volts and things
gravity is one variable that frequency/time  can be used to define.
Although I dont think you will find a frequency/gravity transducer on  
fleabay.
cheers, Neville Michie




On 03/12/2008, at 3:56 PM, Jim Palfreyman wrote:

> 2008/11/29 Mike S <mikes at flatsurface.com>
>
>> At 01:30 AM 11/29/2008, Tom Van Baak wrote...
>>> Note also that clocks at NIST run about 1.8e-13 fast due to the high
>>> elevation of Boulder, CO (general relativity), which is yet another
>>> factor that has to be corrected for compared to the official sea- 
>>> level
>>> definition of the second.
>>
>> Do they really adjust to sea level on earth? That isn't part of the
>> definition. Within that convention, as the mean sea level rises  
>> (~20 cm
>> in the last 100 years), does the length of the second change
>> (relatively)?
>>
>> A clock will run faster the lower the strength of the  
>> gravitational field.
> Even though the mean sea level might rise 20cm in 100 years, it  
> doesn't mean
> the gravitational field is changing in any meaningful way in that  
> time.
> Daily tidal variations would be far greater.
>
> One would assume the definition of the second is in reference to the
> gravitational field at the surface of the mean geoid and has  
> nothing to do
> with sea level.
>
> Jim
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