[ntp:questions] Re: HowTo calibrate system clock frequency using NTP

Daniel Kabs daniel.kabs at gmx.de
Thu Feb 2 09:34:38 UTC 2006

Hello Terje!

Terje Mathisen wrote:
> This is well within the expected precision for such an experiment, the 
> final ntp.drift value (23.2 or 268.3) probably reflects the current 
> drift rate, not the average.
> These two values are different because the environmental temperature 
> varies, often diurnally, so if you log the changes in ntp.drift then 
> you'll probably notice that the average corresponds closely to the 
> 23.7/23.8 numbers.

Did I understand you correctly: You are insinuating that least-squares 
fitting the time offset is getting an average value whereas the 
frequency error (ntp.drift value) represents a "live" value.

I expected it to be the other way round: I thought the frequency error 
is a "slow" value that takes hours or days to converge as a result of 
the control loop phasing in and as such can only slowly react to 
environmental changes (e.g. change in temperature). This contrasts to 
measuring the time offset over a short periode which gives a "snapshot" 
of the current clock drift and as such represents current environmental 

What am I getting wrong here?


More information about the questions mailing list