[ntp:questions] project ntp.br - discrepancy from UTC

Terje Mathisen terje.mathisen at hda.hydro.com
Fri Oct 5 07:15:02 UTC 2007

Antonio M. Moreiras wrote:
> The Cesium clock at observatorio nacional (ON) is UTC. In fact, the ON
> is one of the metrology laboratories that colaborates with the Bureau
> International des Poids et Measures (BIPM) in generating the UTC (as
> NIST does in USA, for example).
> The Rubidium clocks are synchronized with the UTC at least one time per
> year and the manufacturer says that the Rubidum reference has a monthly 
> aging less than 5e-11 and a yearly aging less than 5e-10.
> It gives us a 16ms maximum discrepancy from UTC (31,536,000,000 ms/year 
> * 5e-10 * 1 year = 15.765ms - is this correct?)
> After one year, with the discrepancy at 16ms it will be probabily of the 
> same order than the half round trip time for the majority of the clients.
> Given this, do you you think it will be necessary any modification?


An atomic clock with greater than 1 ms offset isn't really worth it's 
name. :-(

In fact, with such a big slew rate, you would be much, much better off 
with a local GPS receiver to continually tune your Rb source.

- <Terje.Mathisen at hda.hydro.com>
"almost all programming can be viewed as an exercise in caching"

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