[ntp:questions] Single best NTP status indicator of clock accuracy?

David Woolley david at ex.djwhome.demon.invalid
Fri Dec 11 07:56:15 UTC 2009


unruh wrote:

> The root dispersion is an estimate of the error in the remote clock's time. It is not an
> estimate of the difference in time between your clock and the true time.

Although it contains some terms that relate to errors in remote clocks, 
its main component is an estimate of the worst case error in the local 
clock due to worst case frequency errors, assuming evary ntpd is 
actually locked on, between the time the stratum zero clock was read and 
the time that you looked at the statistics on the local machine.  The 
drift calculation potentially uses the drift rate on the machine holding 
the time at the time of the drift, although normally all ntpd's use the 
same rate.

Note, to get the full benefit of this, you need to read the root 
dispersion reported in response to time requests.  I think the value 
given in the statistics doesn't include the component due to the local 
machine.




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