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

David Woolley david at ex.djwhome.demon.invalid
Fri Dec 11 07:49:04 UTC 2009


unruh wrote:

> 
> Offset. That is ntp's best guess as to the difference between the time
> on your clock and the true UTC time. ntp keeps no record of the rate

No.  It is the difference between the time on your clock and the last 
measurement from other clocks.  It includes the instantaneous 
measurement error, but not systematic measurement error.  When ntpd is 
operating in a stable environment and locked onto its sources, the 
instantaneous offset readings can vary widely and the RMS value will be 
quite a bit larger than the RMS variation in error in the actual machine 
clock.

The big argument is about how often ntpd is actually operating in a 
stable environment. When it is out of lock, offset approximates the 
short term part of the error, but still does not include the systematic 
error.




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