[ntp:questions] stupid, simple question about precision
ssimon at domain.invalid
Mon Nov 20 06:20:46 UTC 2006
rgilbert88 at comcast.net wrote...
> Simple Simon wrote:
> > If 'ntpq -c rl' shows the precision of my clock as -20 (roughly,
> > 9ns), does that translate to timestamp confidence interval of +/- of
> > 9ns, or of +/- of 4.5ns) ?
> > Feel free to point to me to the section of the NTP FAQ I've missed,
> > or any other resource that I haven't seen in trying to answer this
> > question on my own.
> > Any guidance greatly appreciated.
> I think you are mistaking precision for accuracy. Precision is the
> measure of the shortest interval your clock can represent. It has
> nothing (or very little) to do with accuracy.
> ntptime will show you the estimated error for your clock. Unless you
> are using a hardware reference clock, the estimated error may be in
> milliseconds rather than microseconds.
After some focused reading of newbie materials, you are right: I am
mistaking precision for accuracy. I appreciate your good manners.
I've seen the estimated error go from 18.3 ms to 3.5 ms since you
reply a few days back. With a vanilla NTP configuration I suppose
I'm not going to see much additional improvement.
My understanding is the best accuracy I might get, on a generic PC
clock, is about 0.050 ms--and that's with SSP and the kernel clock.
Thanks for steering me towards better understanding.
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