[ntp:questions] 500ppm - is it too small?

Richard B. Gilbert rgilbert88 at comcast.net
Thu Nov 12 17:41:13 UTC 2009

Uwe Klein wrote:
> Ulrich Windl wrote:
>> IMHO, most people don't care if their clock is a few minutes off, but
>> with using NTP they suddenly expect that their clock will automagically
>> become as good as an atomic clock.
>> Ulrich
> Afaics it is a question of problem resilience ;-)
> A:
> An off by 1000ppm xtal is not an easy reason
> for exchanging motherboards with your vendor.
> B:
> An off by 1000ppm xtal is differently broken
> from one that wanders up and down the ppm range
> on changes of barometric pressure, humidity and
> other whimms.
> Thus if satisfying timekeeping hangs on 500ppm being
> a limit the next best step is to push on the software.
> "Software" as the word says is regularly the less
> resilient target for problem solving ;-)
> In exchange for brushing off people that ask again and
> again ( with rising levels of displeasure ) the
> more efficient solution would imho be to
> make the ppm limit a configurable option.
> or
> leave the limit and introduce an offset.
> produce obvious error information
> when limits are reached. i.e. forex syslog
> uwe

Do we have any data on just how large a percentage of computer clocks 
are bad enough to exceed the 500 PPM limit?

And is there any reason for NTPD to stand on its head to cope with a 
clock that is broken that badly?

If you really believe that it's an arbitrary limit perhaps you should 
change it to 5,000 or 50,000 in your copy of NTPD and run it for a 
while.  Please let us know how well, or how badly, it works.

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