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

Unruh unruh-spam at physics.ubc.ca
Mon Sep 15 22:10:39 UTC 2008

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

>On 12 Sep, 22:14, David Woolley <da... at ex.djwhome.demon.co.uk.invalid>
>> Howard Barina wrote:
>> > Does an NTP servers take into account it's estimated offset in serving =
>> There seem to have been a lot of questions asked in the last month that
>> are based on the false assumption that "offset" measures the difference
>> between the local clock and true time. =A0Has someone published a
>> misleading document, somewhere?
>I think I am one of the people who has made this mistake.

>> "offset" is the difference between the clients best estimate of the true
>> time and a weighted average of the most recent "best" measurements from
>> its upstream servers. =A0Those measurements have a significant measuremen=
>> error.
>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. 

>How can I obtain a historic record of the difference between true time
>and local clock time on an NTP client?

You need a source for "true time". A gps receiver will give you one with an
accuracy of something like microseconds. 



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