[chrony-users] Accuray statistical claims

[Horia Muntean <horia.muntean@xxxxxxxxx>]

Hi,

I have a stratum 1 NTP server in the same LAN as my client - one
switch apart. The server is a Microsemi SyncServer S600 that gets the
time over GPS and has hardware timestamping on it's port.

On the client's (which is a chrony instance and does not have hardware
timestamping capabilities for NTP) measurements.log the NTP server
reports all root delays and dispersions as zero (0.000e+00).

If on every measurement made by the client and reported on
measurements.log (every 4 seconds), it is true that

abs(offset) + peer_delay / 2 + peer_dispersion <= target

(target being a constant, say 1 ms) is it safe to say with certainty
(100% probability) that my client's system clock has a maximum
divergence from the NTP server's time (which is presumed to be the
source of UTC time when not on holdover) of 'target' (at least when
each measurement was done) ?

If the answer in no, please explain. Any advice about how can this
(prove that a client's system clock is within a target from UTC) be
done only with NTP/chrony ? AFAIK if one wants to measure the accuracy
of a system, another more accurate system must be used (in my case
maybe installing a PPS card on the client then comparing its output
with the server's PPS output) but we can't afford to do this on each
client.

BR

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