# [ntp:questions] Any chance of getting bugs 2164 and 1577 moving?

David Lord snews at lordynet.org
Thu Mar 22 00:16:33 UTC 2012

```Alby VA wrote:
> On Mar 21, 7:36 pm, unruh <un... at invalid.ca> wrote:
>> On 2012-03-21, Alby VA <alb... at empire.org> wrote:
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>>> On Mar 21, 3:55?pm, unruh <un... at invalid.ca> wrote:
>>>> On 2012-03-21, David J Taylor <david-tay... at blueyonder.co.uk.invalid> wrote:
>>>>> "unruh" <un... at invalid.ca> wrote in message
>>>>> []
>>>>>> But -19 is about 2 microseconds if I understand it correctly. That means
>>>>>> that the clocks are incapable of delivering more than about 2
>>>>>> microseconds of accuracy. What is you ?that last decimal digit of
>>>>>> accuracy in the offset is thus pure noise-- dominated by clock reading
>>>>>> noise. Why is it important for you then?
>>>>> When I can see the decimal places, then I will know whether the precision
>>>>> estimate is reasonable. ?Just getting values such as -1, 0, 1 microseconds
>>>>> is insufficient to make that call.
>>>> And how will the extra decimals help? The -19 was determined by making
>>>> successive calls to the clock and seeing how much it changed between
>>>> successive readings. That gives a good estimate of how long it takes to
>>>> make a call to the clock. Any precision in the answer beyond that is not
>>>> accuracy. I could give you the time to 60000 decimal places, each one of
>>>> the diffetent, but the last 5995 just being garbage (random numbers)
>>>> Would that tell yo uanything?
>>>> If for some reason you do not believe ntpd's estimation of your clock
>>>> accuracy, develope a better algorithm for determining it. It is a bug is
>>>> ntpd is reporting an accuracy much worse than it actually is.
>>>> Ie, you have no data to make that call even if you get more digits.
>>>>> David
>>> unruh:
>>>   My take is the precision output might say your device is -19 so you
>>> know its
>>> accuracy is around 2/microseconds. But the offset several decimal
>>> places
>>> allows you to see its ever changing accuracy within that 2/microsecond
>>> band
>> But that is not accuracy. That is presumably (if that -19 is accurate
>> and not a bug) is simply noise. If your measurement technique is only
>> good to 2us, then any additional precision is just noise. It may be fun
>> to see the noise, but not terribly useful. If it is not noise, then that
>> -19 is wrong, and one has a bug in the determination of the accuracy of
>>
>>> to a greater detail than just -1, 0, or 1 microseconds. I guess its
>>> just a matter
>>> of getting more granular details for cool MRTG charting. :)
>> It could well be that charting looks better without just bands on the
>> page. But is it worth it if that detail is just junk? It certainly is
>> not great art.
>
>
>  It there any good way to determine what is noise and what isn't?
>

ntpq -c rv gives output including precision= , which on
my server indicates precision=-19 which is 1/(2^19) or
approx = 2us

David

```