[ntp:questions] 500ppm - is it too small?
Richard B. Gilbert
rgilbert88 at comcast.net
Thu May 7 16:23:18 UTC 2009
David J Taylor wrote:
> I've recent been suggesting the Windows port of NTP as a program
> suitable for an application where the timekeeping needed to be within a
> second or two. Yes, NTP is overkill, but it has the advantages of
> multiple servers, best server selection, adaptive poll rate, and memory
> of the clock drift etc. However, on quite a few installations - at a
> guess between 1% and 5% - NTP has failed because the click frequency
> error appears to be too great for NTP to correct.
> Is there any feeling for changing the 500ppm limit, perhaps to 1000ppm
> or even as much as 5000ppm (to pull a figure out of the hat)? Or is
> 500ppm generally believed to be the worst error which should be
> One possibility is that some of the problem PCs are portables, with some
> sort of power-saving or even hibernation scheme. I don't have direct
> visibility of the type of PC.
An error greater than 500 PPM suggests seriously broken hardware! There
might be some way to "kludge" the software to compensate for this
brokenness but I think it would be easier and cheaper to fix or replace
the broken hardware.
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