[time-nuts] Allan Deviation recipe?
hmurray at megapathdsl.net
Tue Jul 19 17:28:32 EDT 2016
[You sent that to 3 lists that I'm on. I'll reply here.
I think your X axis is off. Your left edge is 1 second and you don't have
data for that. peerstats is every 64 seconds. (unless you mucked with
maxpoll) I'm guessing the software you used is assuming they are every
second. There may be a command line parameter.
The normal ADEV is V shaped. The left slope is noise in the readings. The
right slope is drift in the clock. That assumes you have a good reference
clock, where good means much better than the DUT.
In this case, there is no long term drift since ntpd is tracking GPS. You
will probably get a traditional V if you disable ntpd. That will turn things
inside out. Your DUT will be good (GPS) and your reference clock (PC) will
There is probably a simple way to do that but I can't think of it. I would
try adding noselect to all the servers and refclocks, and add a localclock if
you want to monitor that box from other systems.
There is a slight step in the NMEA data at 1000 seconds and maybe a similar
step in the PPS data at the right edge of the graph. I don't know what that
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