[time-nuts] Testing frequency using NTP Bruce GPS ps
wb6bnq at cox.net
Sat Oct 4 03:43:16 UTC 2008
Mike Monett wrote:
> > For more detail see:
> > http://tf.nist.gov/timefreq/service/fms.htm
> Thanks very much for the link. It is curious they don't seem to
> spend much effort on correcting the user's frequency errors. They
> just want to report how much they are off.
> Why is that? You'd think they would perform a more valuable service
> by applying advanced techniques to adjust the user's equipment to
> minimize the error, then report and certify the actual result. Is
> there some reason they want to leave the user's equipment
One of the worst perturbations is that of man himself. Unless one is highly
knowledgeable of the effect of an adjustment, usually the act of the adjustment
is worst then if it had been left alone.
In the world of the "Primary masters," they do not make adjustments, only compare
differences and then report those differences. Typically, the standards that are
inter compared are of such high quality construction that adjustment is neither
possible nor wanted.
For inter comparisons, a device of known quality is measured before it starts its
journey around the labs, of course it is measured at each lab and then upon
return is measured again at the lab where it all started. No human adjustment is
ever performed. This way mostly just environmental factors influence the
portable reference device and much of that can be mitigated with careful record
keeping during its trip.
In the case of the "FMS" you mentioned, the only difference is the devices being
compared are not being moved. The same methodology still applies however.
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