[ntp:questions] Why does GPS time diverge from system time?

Chris Albertson albertson.chris at gmail.com
Sat Apr 14 01:51:17 UTC 2012

On Fri, Apr 13, 2012 at 12:01 PM, Charles Elliott <elliott.ch at verizon.net>wrote:

> ...   The
> average offset since the restart from the offsets computed by NTPD and
> output in the loopstats file is -0.054193 (ms), while the stdDev is
> 1.507155.  The maximum and minimum offsets are about +5 and -5 ms,
> respectively, while the overwhelming majority of offsets are between +- 3
> ms.

If you are running Windows with a USB connected GPS, I'd say your
performance is good.  Better than some others have reported using that

You said the GPS and system times were monotonically diverging.  I don't
see that from the numbers you post.  To prove that you'd need to measure
system and GPS times every couple hours for several days.   I think the
difference you are seeing is just the expected noise.

Again for Windows and a USB connected GPS +5 and -5 ms is more or less what
you should expect.


Chris Albertson
Redondo Beach, California

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