[ntp:questions] FW: Clock Offset

Mischanko, Edward T Edward.Mischanko at arcelormittal.com
Sun Dec 23 02:06:11 UTC 2012


> -----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 David Woolley
> Sent: Saturday, December 22, 2012 6:14 PM
> To: questions at lists.ntp.org
> Subject: Re: [ntp:questions] FW: Clock Offset
> 
> unruh wrote:
> > On 2012-12-22, Mischanko, Edward T
> <Edward.Mischanko at arcelormittal.com> wrote:
> 
> >> 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.
> 
> I don't believe he is now comparing the overall estimate with
> the most
> recent individual measurements.  I think he is comparing the
> best
> estimate for an individual source, with the ntpq peers, most
> recent
> offset for that source.
> 
> The formula for an individual filtered offset is something like:
> 
> (z  ^ n) * Offset
> 
> where z is the Z-Transform operator and n is an natural number
> <= 7,
> such that (z ^ n) * estimated-offset-error  is minimal.   Of
> course, it
> is not described that way in the actual code, and I don't think
> it is
> described that way in the documentation.
> 
> I believe the error estimate includes the round trip delay, and
> the
> stratum, but it is that sort of thing that is subject to change.
> 
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[Mischanko, Edward T] 

David, 

Thank you for your time in explaining this to me.  Unfortunately, my mathematics education stopped at intermediate algebra; it appears that the formula is in calculus?  Anyway, I feel like I have beaten this horse to death.  I can accept the fact that they are different and yet notice their similarities. I'm not sure Unruh completely understands my point?

Regards,
Ed 



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