On Mar 21, 8:16 pm, David Lord <sn...@lordynet.org> wrote: > Alby VA wrote: > > On Mar 21, 7:36 pm, unruh <un...@invalid.ca> wrote: > >> On 2012-03-21, Alby VA <alb...@empire.org> wrote: > > >>> On Mar 21, 3:55?pm, unruh <un...@invalid.ca> wrote: > >>>> On 2012-03-21, David J Taylor <david-tay...@blueyonder.co.uk.invalid> > >>>> wrote: > >>>>> "unruh" <un...@invalid.ca> wrote in message > >>>>>news:itmar.5841$yd7....@newsfe15.iad... > >>>>> [] > >>>>>> 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 > >> the clock reading. > > >>> 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
Yup. I'm getting the same thing, precision = -19 In the math, I get 0.0000019073486328125 (1.907/microseconds). To improve this to better precision, would the only path of success be in getting a better stratum 0 device? assID=0 status=0415 leap_none, sync_uhf_clock, 1 event, event_clock_reset, version="ntpd 4.2.6p5@1.2349-o Mon Feb 20 22:00:33 UTC 2012 (1)", processor="amd64", system="FreeBSD/9.0-RELEASE", leap=00, stratum=1, precision=-19, rootdelay=0.000, rootdisp=0.297, refid=PPS, reftime=d314f812.ee1ec4ca Wed, Mar 21 2012 21:00:02.930, clock=d314f817.b13ef313 Wed, Mar 21 2012 21:00:07.692, peer=21829, tc=4, mintc=3, offset=0.002, frequency=-24.569, sys_jitter=0.002, clk_jitter=0.002, clk_wander=0.001 _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
