Garmin GPS 12 - TRIP accuracy?

I've learned to disregard the Trip reading at the end of my walks, as
it always reads significantly low. If there are any other
walkers/hikers here, I'd be interested in knowing what error they
typically get.

Today's walk, shown in both Memory-Map and GPS Utility as 15.8 miles,
was 13.6 according to my GPS 12. So the actual was 16% higher than
reported, and that's fairly typical of my walks.

I'm still not clear *why* the error arises. The track seems
continuous. If PC programs can get it right, why can't the Garmin?

--
Terry, West Sussex, UK

On Sat, 14 Apr 2007 18:18:07 +0100, Terry Pinnell



You have the GPS set to display distance in nautical miles.

15.8 * 5280/6076 = 13.7


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

No, I don't, it's set to Statute. (I think I might just have spotted
that over 5 years or so!)


Pure coincidence.

--
Terry, West Sussex, UK

On Sat, 14 Apr 2007 20:15:30 +0100, Terry Pinnell


Don't be so quick to discard an explanation that fits your facts! This
explanation fits way too nicely to be "pure coincidence".

Rather than "You have the GPS set to display distance in nautical
miles" you can think "the thing's calcs are using nautical rather than
statute."

There could easily be a bug that uses Nautical mile values rather than
Statute. Perhaps Garmin got the values swapped, or the same value is
used in both statute & nautical calcs. I imagine that changing
settings will directly change the displayed values - it would be easy
to check. Maybe you're the first one to discover the bug.

Terry Pinnell wrote:

None detectable with my GPS-V.



Why do you think the PC programs are correct? How old is your GPS 12?
I don't have a GPS 12 so I can only relate my experience with my GPS-V
and my previous unit, a GPS-II+. The GPS-II+ ignored points when I was
moving very slowly (the II+ dates back to when we still had SA). This
meant that a steep switchback could appear as a straight line between
two points. This would make the GPS odometer read low. Try walking
very slowly for a 10 or 20 meters and see what it does.

What setting do you have for your track log setup? Specifically how
often to record a point? The V allows me to select a particular Distance
in increments of 10m, Time in increments of 1 s or Auto with a choice of
resolution described by Highest, High, Medium, Low or Lowest. I use
usually use Highest.

I don't have either of the programs you mention since I don't use
Windows but I have my own program to give detailed track information
from a saved or active track or tracks. I happen to have not yet reset
my GPS from a trip downtown the other day that involved both driving and
walking. The GPS odometer says 42.6Km. My program says 42.56 Km which
rounds to 42.6.

Another source of error a friend encountered was he was using "Power
Save" mode. This mode saves power by reading position less frequently
and assuming straight line segments between. I would expect that this
would affect the programs and the GPS equally.

I hope this gives you some clues as to what the problem is.

Ted