[time-nuts] NTP, PPS and < 10 us offsets

Hal Murray hmurray at megapathdsl.net
Wed May 15 03:51:07 EDT 2013


albertson.chris at gmail.com said:
> Maybe not you, but I think some people think "Oh my, NTP is not checking the
> time very often.  It must not be accurate."   That is thinking backwards,
> you need the long poll interval to see small errors in rate.   But this
> assumes a stable local clock.  NTP balances this. 

That "balance" is assuming a classic ADEV type V curve.  That assumption 
works better in old non-green systems that burned lots of power in an idle 
loop when they didn't have any work to do.  With modern systems, it's easy to 
change the temperature significantly by starting/finishing a big chunk of 
work.

External temperature changes can also be important.  Every now and then, I 
like to repost this link.  This seems like a good opportunity.
  NTP temperature compensation
  http://www.ijs.si/time/temp-compensation/



-- 
These are my opinions.  I hate spam.





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