Daniel,
You might get a better understanding of the error model from the
briefings at the NTP project page. The statistic of interest is the
Allan variance, which describes the clock frequency stability as a
function of averaging time.
Dave
Daniel Kabs wrote:
Hello Professor Mills!
Apropos engineers: any engineer strives for high precision measurements
and thus tries to minimize uncertainty to a reasonable level. So for any
method of measurement the magnitude of uncertainty has to be determined
and valued. That's what I am trying to do currently :-)
Enter Plan B: You suggested to "record the time of day and the offset",
without saying how you'd record the time. So I tried different methods
(for "recoding the time") and found
cron : 23.40 s = 270.83 PPM
reftime: 23.35 s = 270.25 PPM
org : 23.30 s = 269.67 PPM
rec : 23.29 s = 269.56 PPM
Mh, maybe I should have converted the values to PPMs earlier! They look
much nicer now. Leaving out the "cron job", they agree within +/- 0.5
PPM. Of course, this should be backed by repeating the "experiment" and
checking how the values scatter (disperse? I'm don't know the proper
English word here).
You are right, this uncertainty is reasonable. So I should stop bugging
you about timestamps :-)
Mission accomplished! Thanks.
Bye now,
Daniel
David L. Mills wrote:
Daniel,
Have you considered what an engineer means by "almost exact?" There is
always an uncertainty in any physical measurement. Yours is no exception.
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