Re: [chrony-users] How to plot statistics to show tracking accuracy?

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On Mon, May 07, 2012 at 05:06:55PM +0100, Ed W wrote:
> So my theory is that gpsd is measuring the timestamp of the end of
> the ZDA sentence (and working that back to get the initial
> timestamp) and this gives an additional 0.5-1ms jitter that might
> not be there if we measured the timestamp of the initial $.  If so
> then I might expect to see a jitter distribution which is positively
> skewed (every time the last character drops into a later 1ms read)
> Can someone give some guidance on the correct statistics to plot to
> investigate this further?  I'm a little unsure on how to interpret
> the stats in /var/log/statistics.log also /var/log/tracking.log
> seems interesting?

I think the best data for this investigation are the actual offsets
measured by the refclock driver, i.e. cooked offset in the refclocks
log. The dispersion of the filtered sample (- in raw offset) could be
perhaps interpreted as a jitter divided by some small constant.

The tracking log is more about the local clock and the statistics log
is from already filtered data from refclocks.

Miroslav Lichvar

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