[time-nuts] Primary standard again

[Lux, Jim (337C)]

> 
>     ** Primary means that the clock will meet its spec without being "calibrated" against a better
> clock**
> 
>     From your definition a Rb can be a primary standard for a 1e-6 world and a crystal as well as my
> wrist watch
> can be a primary standard in a 1e-3 spec or whatever  they can repeat without Calibration.
> BUT I have not heard anyone argue that any of the above are primary standards, even at some reduced
> spec.
> (maybe just because not cost effective?)
> 

I suppose a pendulum can be a primary standard at some accuracy.  Using the "kit of parts" analogy, if one builds the pendulum and operates it at sea level, the period of the pendulum is entirely determined by the physical dimensions and the gravitational constant.