[time-nuts] Allan Deviation recipe?

Hal Murray 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 
drift.

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 
means.



-- 
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