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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] understanding tracking.log
- From: Bryan Christianson <bryan@xxxxxxxxxxxxx>
- Date: Wed, 22 Jul 2015 02:32:49 +1200
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Thanks for clearing that up Miroslav. Makes sense to me now. I am working on a Mac OS program that will graph the logs and was having trouble reconciling the values.
> On 21/07/2015, at 11:19 pm, Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
>
> On Tue, Jul 21, 2015 at 08:23:10AM +1200, Bryan Christianson wrote:
>> In looking at /var/log/tracking.log I see
>>
>> Date (UTC) Time IP Address St Freq ppm Skew ppm Offset L Co Offset sd Rem. corr.
>> ==================================================================================================
>> 2015-07-20 20:13:34 10.64.1.25 2 30.665 0.177 -3.530e-06 N 2 6.553e-05 1.151e-05
>>
>> I am having trouble understanding the field 'Offset sd' and what i represents. It is consistently an order of magnitude greater in value than the 'Offset' field so I presume it is not the standard deviation of offset.
>
> Yeah, I agree this may be confusing. The offset sd value is meant to
> be an error estimate of the offset, it's not actually calculated from
> the values printed in the offset column.
>
> It's the estimated deviation of the intercept from the linear
> regression. Depending on how well the clock tracks the source, it may
> be consistently larger or consistently smaller than the offset value
> (or its RMS value in the chronyc tracking output).
>
> The other reason why it may be significantly larger is that when
> combining sources (Co > 1 in the tracking log) it also includes the
> offset between the combined sources. So even if each source is
> perfectly stable, their offsets may not be very close and the offset
> sd value will still be large.
>
>> "chronyc tracking" displays a result for RMS Offset consistent with 'Last Offset' as seen here:
>>
>> Reference ID : 10.64.1.25 (fleur.lan.seaviewsound.co.nz)
>> Stratum : 2
>> Ref time (UTC) : Mon Jul 20 20:20:34 2015
>> System time : 0.000007302 seconds slow of NTP time
>> Last offset : +0.000004646 seconds
>> RMS offset : 0.000005560 seconds
>
> --
> Miroslav Lichvar
>
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