On Wed, 2008-10-01 at 20:48 -0400, Scott McGrath wrote: > It depends on how accurately you want to measure the oscillator > frequency with your approach short term you probably would not be able > to measure the oscillator offset any better than a few parts in 10-5 > longer term probably a few parts in 10-7 might be possible as you > could compute the allen deviation and fit a curve through the median > values. > > NTP from a stratum 3 clock is only going to be precise to a few > milliseconds and for meaningful accuracy you need another order of > magnitude. This is part of the function of the drift file in xntpd > in which the daemon attempts to compensate for the drift and offset > inherent in cheap oscillators used in computer applications. >
You do not have to chose a bad NTP server. With better servers you can gain a few orders of magnitude. $ ntpq -p timehost.lysator.liu.se remote refid st ... delay offset jitter ================================================================ *GENERIC(0) .GPS. 0 ... 0.000 0.014 0.002 +nissan.ifm.liu. .PPS. 1 ... 0.651 0.000 0.035 +ntp1.sth.netnod .PPS. 1 ... 3.667 -0.018 0.052 +ntp2.gbg.netnod .PPS. 1 ... 10.967 -0.010 0.014 -ntp1.mmo.netnod .PPS. 1 ... 13.899 -0.077 0.061 Also look at the NTP temperature compensation discussion at http://www.ijs.si/time/temp-compensation/ -- Björn _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.