Re: [chrony-users] Root delay and Root dispersion values in `chronyc ntpdata'

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Thu, Aug 10, 2017 at 01:22:25PM +0300, Horia Muntean wrote:
> The root dispersion just after a clock update contains what the server
> reports right ?

It includes dispersion that accumulated since the best measurement was
made (it doesn't have to be the last one) and also peer dispersion of
the measurement.

> In my opinion the values (root delay end dispersion) taken just after
> the clock update
> along with a short update interval (less than few seconds) would give
> a good max. error estimate.
> In a short amount of time between the updates the root dispersion
> should not increase too much.

If the network is heavily loaded, chronyd may drop a large number of
consecutive measurements.

I think what people are interested in is the maximum possible error of
the clock at any time, not just the points when the clock was updated.

If we know at time t the error was 10 +/- 50 microseconds and at time
t+100 (seconds) it was -20 +/- 70 microseconds, what can we say about
t+1, t+50 and t+99, if we assume the frequency of clock is accurate to
1 ppm?

-- 
Miroslav Lichvar

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