[ntp:hackers] Re: loopstats log - Allan deviation truncated decimal places?

David L. Mills mills at udel.edu
Thu Dec 23 20:19:47 PST 2004


Mark,

This was purposely done, as the digits below 10e-9 are meaningless in a 
nanosecond clock. The precision corresponds to the frequency precision, 
which is also 10e-9.  The former representation was 10e-12, which is 
ludicrous. The implication is that what you see below 10e-9 is 
significant only if you pretend a picosecond clock. You will note the 
value sometimes appears at  .000, which is also intentional and tells 
you that the Allan deviation estimate is probably more affected by the 
noise floor than valid measurements. It's really important in this 
business to avoid drawing conclusions from what is really 
fourserbaliwhiganoi*.

Dave

* Fourier series bandlimited white Gaussian noise. Pronounce it as one word.

Mark Martinec wrote:

>I noticed my recent loopstats logs show only three decimal places for the
>sixth field (next to last)  in loopstats log, which when plotted, gives only a 
>couple of discrete horizontal levels:
>
>53362 86324.291 0.000999703 1.286 0.000515561 0.002 6
>53362 86386.299 0.000059720 1.286 0.000648263 0.001 6
>53363 103.291 0.000834551 1.292 0.000682111 0.003 6
>
>There used to be 6 decimal places in my earlier logs,
>and the web page shows example with 7 decimal places:
>
>  loopstats:
>  Enables recording of loop filter statistics information. Each update of the
>  local clock outputs a line of the following form to the file generation set
>  named loopstats: 
>    50935 75440.031 0.000006019 13.778190 0.000351733 0.0133806 
>
>  (and is missing the 7th field)
>
>I think adding back two or three decimal places makes more sense
>on the plot, although I'm not arguing if these additional decimal places
>may or may not be significant.
>
>  Mark
>  
>




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