[time-nuts] Yb clock - stability estimation procedure?

[Magnus Danielson]

Hi,

On 08/26/2013 01:56 PM, Bob Camp wrote:
> Hi
>
>
> On Aug 26, 2013, at 2:01 AM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>
>> Exactly. As you have three devices, measuring them pair-wise you get
>> three measures and three un-knowns, and you can untangle the
>> stability of each individual. If you have yet more, you can get some
>> confidence levels also as it becomes overdetermined. 
> The only real gotcha is common mode drift. If all your gizmos are made same place / same time / same parts then they may drift the same way. In this case "drift" could correlate to environment rather than just to time (aging). Back when HP pretty much made all the Cs standards this was a common thing to worry about when setting up an ensemble of them. 
Indeed. An independent source make sense, like a different atomic
reference mechanism, or as you propose, a different location.
> Of course you could always move your ensemble to an un-inhabited cave and …..
>
> No, HP did not make the long tube Cs standards at NIST (as the NIST guys always love to point out) and they are very different animals than the ones you can buy. So, the international definition of the second has always been safe from manufacturer induced common mode. 
Also, it wasn't as manufacture dominant as it has been. Not all the
commercial cesiums being used have been HP, even if HP have made a big
number of their dominance.

Cheers,
Magnus