[ntp:questions] Server offset included in served time?

David Woolley david at ex.djwhome.demon.co.uk.invalid
Tue Sep 16 07:32:49 UTC 2008

Unruh wrote:
> Mike K Smith <mks-usenet at dsl.pipex.com> writes:

>> So I can't plot the offsets in the loopstats file to show how accurate
>> the time was on an NTP client over a period of time?
> That is the best estimate that you have. Alternatively buy a GPS hook it up
> and measure the offset against that. 

But, if you use individual measurements, you will get a figure that, 
most of the time, is several times the true error and not necessarily in 
the right direction.

What you can do, is to use some hindsight, and make a slightly better 
estimate of the true time by combining offsets from both before and 
after the time the local clock was read.  That gives you an advantage 
during startup and after transients, but, in the steady state, the local 
clock time is going to be the same as such an enhanced statistic.

In the steady state, all you can really deduce from the offsets is the 
amount of noise in the measurements.  You can then expect the amount of 
noise in the local clock time to be several times less.

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