[ntp:questions] Tracking the drift of a GPS clock relative to a HW clock
Unruh
unruh-spam at physics.ubc.ca
Wed Jan 21 17:19:19 UTC 2009
David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:
>ryad.bek at gmail.com wrote:
>> This algorithm is robust because it is based on
>> special techniques (it uses common packets in the traces to provide
>> synchronisation).
>In the end, any such algorithm is going to have to use techniques
>similar to ntpd or chrony's. The one advantage is that it is
>retrospective, and therefore probably better matches chrony's linear
>regression approach. (NTP uses a low memory, incremental algorithm.)
That is why ntp has a VSZ of 4460 vs 2189 for chrony and RSS of 940 vs 748
for chrony:-)
>A better example of this sort of problem, for this newsgroup, is
>probably that of deriving UTC from historical information on the
>individual clocks that contribute to UTC.
But he also does not realise that the unconstrained computer clock would
soon be out by seconds (in a day) minutes, or even hours.
>I've also done this sort of thing on data with rather larger jitters and
>the main error due to sloppy eyeball and wristwatch time setting
>(performed at not well controlled times) on specialist (although rather
>common) equipment, that doesn't support NTP.
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