[time-nuts] Primary Time Standards

[Will Matney]

Jim,

It is my understanding that the government standard offices around the
globe, like NIST, calculates time by the earths rotation, I guess you could
say, the old way, or using astronomy, but with this, they use things like
the decay factors of atomic materials to keep this time. If I recall,
things had to be recallibrated after the earthquake at Japan, as it changed
the earths rotational speed a very minute amount. Its kind of like, which
came first, the chicken or the egg on the standards.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 7/14/2011 at 12:26 PM Jim Palfreyman wrote:

>Hi All,
>
>I've just realised I don't understand something. Something quite basic.
>
>Primary Standards are ones which don't have to be calibrated against
others.
>My understanding is that Caesium and Hydrogen masers are Primary Standards
>(in our field).
>
>Secondary Standards are calibrated against the Primary Standards. My
>understanding is that Rubidium is an example of a Secondary Standard.
>
>So I can calibrate my Rubidium clocks by adjusting the C Field. All good.
>
>But why is it that Caesium Clocks and Hydrogen Masers have an adjustment
>facility?
>
>And what about the clocks used to determine UTC around the world? Do they
>have an adjustment facility? What are they adjusted to? Wouldn't that make
>them Secondary Standards?
>
>Now I'm aware that the "average" of those clocks is UTC, so are those
clocks
>adjusted regularly to get closer to that average?
>
>I'm sure someone can clear this up for me.
>
>Regards,
>
>Jim
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