[ntp:questions] FW: Clock Offset

unruh unruh at invalid.ca
Sat Dec 22 22:51:01 UTC 2012


On 2012-12-22, Mischanko, Edward T <Edward.Mischanko at arcelormittal.com> wrote:
>
>> -----Original Message-----
>> From: Mischanko, Edward T
>> Sent: Friday, December 21, 2012 9:14 PM
>> Subject: RE: [ntp:questions] Clock Offset
>> 
>> 
>> > -----Original Message-----
>> > From: questions-
>> > bounces+edward.mischanko=arcelormittal.com at lists.ntp.org
>> > [mailto:questions-
>> > bounces+edward.mischanko=arcelormittal.com at lists.ntp.org] On
>> > Behalf Of Terje Mathisen
>> > Sent: Thursday, December 20, 2012 2:42 AM
>> > To: questions at lists.ntp.org
>> > Subject: Re: [ntp:questions] Clock Offset
>> >
>> > Mischanko, Edward T wrote:
>> > > No local clock is in use!!  I was really questioning how the
>> > > averaging algorithm could come up with a negative offset
>> when
>> > none of
>> > > the individual offsets were negative?
>> >
>> > That's (sort of) easy!
>> >
>> > The local clock offset is the best estimate of the
>> > (exponentially afair)
>> > averaging algorithm from the individual iterations of the
>> > control loop,
>> > while the ntpq -p gives you the last measurement from each
>> > server/clock
>> > source.
>> >
>> > I.e. they measure different things.
>> >
>> > Terje
>> > --
>> > - <Terje.Mathisen at tmsw.no>
>> > "almost all programming can be viewed as an exercise in
>> caching"
>> >
>> > _______________________________________________
>> > questions mailing list
>> > questions at lists.ntp.org
>> > http://lists.ntp.org/listinfo/questions
> [Mischanko, Edward T]
>
> Terje,
>
> I do not doubt you, but if they are measuring different things
> to represent the same thing, then there is a formula off
> somewhere?

No, they do not "represent the same thing". They are different things.
One is the instantaneously measured offset between the local clock and
the servers. The other is the best estimate ntpd has for the difference
between the local clock and true UTC time. 

>
> Ed



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