[time-nuts] Primary Standards...

[Mike S]

renamed, since the discussion has shifted.

NIST gives this definition:

"Primary Standard

"A standard that is designated or widely acknowledged as having the 
highest metrological qualities and whose value is accepted without 
reference to other standards of the same quantity. For example, NIST-F1 
is recognized as a primary standard for time and frequency. A true 
primary standard like NIST-F1 establishes maximum levels for the 
frequency shifts caused by environmental factors. By summing or 
combining the effects of these frequency shifts, it is possible to 
estimate the uncertainty of a primary standard without comparing it to 
other standards.

"In the time and frequency field, the term primary standard is 
sometimes used to refer to any cesium oscillator, since the SI 
definition of the second is based on the physical properties of the 
cesium atom. The term primary standard is also commonly used, at least 
in a local sense, to refer to the best standard available at a given 
laboratory or facility."