On 2020-06-15, David Woolley <david@ex.djwhome.demon.invalid> wrote: > On 15/06/2020 15:38, David Taylor wrote: >>> >>> https://www.eecis.udel.edu/~mills/ntp/html/cluster.html > > What is the clock resolution? If you try and measure jitters that > aren't several times the resolution, they are not going to be > particularly valid. > > If the hardware clock is almost dead on, and the peak to peak dither is > just less than the resolution, there will be long periods in which it > will read as as zero, even though it is actually close to one resolution > unit. You could also get cases where dither was very low but read as > one resolution unit for long periods. In fact, if it was possible to > find tune the actual clock oscillator, during an ideal lock you would > have peak to peak dither, as measured, of one or two resolution units, > even though the actual phase noise was much less.
>From his graphs this sure seems to be what is going on. The changes in the clock seem to all have 1/2 us resolution, while the clock seems to have 1us resolution. > > (Arguably, a jitter that is less than the clock resolution will result > in worse time accuracy than one that a few times it, as the clock > resolution will not be dithered out. > > That makes the, normally unrealistic, assumption that the systematic > error is less than the clock resolution.) _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions