[time-nuts] NPR Story I heard this morning

Tom Van Baak tvb at LeapSecond.com
Mon Nov 3 17:27:21 EST 2014

> 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.


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