Hi Ken,
That's correct. No two clocks ever agree. If they look like they do, you are
not looking close enough or not waiting long enough.
That's also why UTC is based on the combined stability of hundreds of clocks.
The weighted average of many cesium clocks is known to be better than any one
cesium clock. So a big part of the UTC infrastructure is the inter-comparison
of clocks all around the world. Another part is then slowly adjusting local
standards to follow the more accurate global mean.
You'll notice too, that many postings to this list are not just about clocks,
but also precise time measurement, and about disciplining. Whether UTC at a
national lab or a GPSDO at home, there is clock, measurement, and gradual
adjustment.
/tvb
----- Original Message -----
From: ken hartman
To: Tom Van Baak ; Discussion of precise time and frequency measurement
Sent: Monday, November 03, 2014 2:52 PM
Subject: Re: [time-nuts] NPR Story I heard this morning
Not to put too fine a point on it, but my practical understanding is that any
two or more clocks generally do *not* agree (that is - yield identical
phase/frequency information) ever, anyway. So atomic horology - and beyond -
means that we continue to ?adjust? ?compensate? clocks of whatever stability
and accuracy to the current, agreed upon "ideal" - even as the ideal may move
or evolve.
On Mon, Nov 3, 2014 at 4:27 PM, Tom Van Baak <t...@leapsecond.com> wrote:
> I don't see anything in the BIPM definition of the second regarding sea
level.
Hi Mike,
The usual wording for the definition of the SI second also includes the
word "unperturbed". That little word covers a host of physics and engineering
effects and can keep graduate students busy for years. You either have to
eliminate them from your clock or your lab, or extra carefully measure then and
back-out their effects on your clock's operating frequency.
For a really good example of the sort of corrections that are made inside a
cesium clock see: http://tf.nist.gov/general/pdf/1497.pdf
By the time you read to page 30, you'll see table 3 and 4 which summarize
the perturbing corrections.
/tvb
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
