[ntp:questions] Comparing offset of multiple refclock/servers

John Ackermann N8UR jra at febo.com
Mon Aug 15 00:05:44 UTC 2005

As part of my timekeeping fixation, I just put three FreeBSD-based NTP
servers online on my home network, each driven by its own refclock (two
HP Z3801A GPSDOs, and one Spectracom 8170 WWVB clock).

In addition to plotting the internal offset and jistter performance
(which I have on-line at http://www.febo.com/time-freq/ntp/stats), I'd
like to compare and plot the relative offset of the three systems
against one another.  It seems like that should be easy, but I'm having
some trouble figuring out the best way to go about it, since even the
PPS sources may show a slight offset in the ntpq -p results, and of
course if one of the refclocks has an offset (e.g., right now my WWVB
clock has about 3ms of systemic offset), the server that relies on it
won't directly show that -- it won't know that the time it's syncing to
is a little bit off..

One option might be to go to a fourth machine that is looking at these
three, and use it as a sort of transfer standard -- looking at the
relative offset of other machines, and then subtracting them against
each other to obtain the differences.  But that seems sort of klunky.

Am I missing something obvious?  Any suggestions would be appreciated.



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