[ntp:questions] Garmin 18 LVC: whether to fudge

Steve Kostecke kostecke at ntp.org
Wed Feb 11 18:37:12 UTC 2009

On 2009-02-11, shane-dated-1234940584 at csy.ca wrote:

> I'm using a Garmin 18 LVC connected using LinuxPPS with mostly good
> results. I am curious about one thing though. The offset reported by
> the GPS18 differ from the public NIST servers by around 1.7-1.9MS. as
> shown in the offset numbers of ntpq below.
>      remote       refid st t when poll reach  delay offset jitter
> *GPS_NMEA(0)     .GPS.   0 l    4   16  377   0.000 -0.448  0.189
> +bigben.cac.wash .USNO.  1 u   34 1024  377  11.134  0.283  2.645

The offset difference in your _snapshot_ is only 0.731 milliseconds.

If you wich to calculate a correction value you need to look at the
statistics over the long term. Enable statistics collection, let ntpd
run for a few days, and use the peer.awk script from the ./scripts
directory of the NTP Reference Implementation Distribution to summarize
your peerstats file.

Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/

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