[ntp:questions] Keeping NTP Honest Redux
unruh-spam at physics.ubc.ca
Wed Nov 11 23:01:12 UTC 2009
David Woolley <david at ex.djwhome.demon.invalid> writes:
>> David Woolley <david at ex.djwhome.demon.invalid> writes:
>>> Looking at the graphs, one needs the first derivative of the rate, as well.
>> Why? If you want the details of how chrony works, I could supply it, but it uses
>Because most of the time the first derivative is almost constant, which
>will force an adaptive linear regression to use a very short baseline.
Sorry. If the first derivative is almost constant, chrony will grow the baseline
out to its max extent (64 data points). It is only when the first derivative
changes rapidly that the baseline is shortened. In typical use, the baseline is
about 15 to 20 points.
(chrony runs a test-- using the number of times that the residual changes sign-- to
determine if the linear regression is statistically good or not.
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