[ntp:questions] Remarkably good CPU oscillators?

Hal Murray hmurray at suespammers.org
Sun Nov 5 18:13:12 UTC 2006

In article <T1162744621 at djwhome.demon.co.uk>,
 david at djwhome.demon.co.uk (David Woolley) writes:
>In article <1162738456.358848.206590 at h48g2000cwc.googlegroups.com>,
>shoppa at trailing-edge.com wrote:
>> Is this statistic just "too good to be true"? Or did I luck out when I
>> bought this box many years ago?
>No. If anything it is bordering on the too big to be good.  This is
>one of the main reasons why I think that ntpd should be much more reluctant
>to apply corrections of more than about 3 to 5 ppm, once the frequency has
>been calibrated.  My feeling is that it should limit the corrections to
>this range unless there is an extended period indicative of a different
>frequency.  It might be reasonable to allow, say, 0.1ppm per day to 
>account for long term drift.

The short term drift depends strongly on the temperature.
The big spike on the pink at -14 and -38 is the self heating
on the CPU crystal from a big cron job.
The small blue spike is the self heating on the crystal
driving the TOY clock.

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