position accuracy question

Hi all,

My eTrex Vista HCx surprised me today. Normally when I'm out and
about in my local area the display shows no noticeable uncertainty
ring--I also run the CNNA map, about a 2009 version.

I'm just back from a trip to the UK, and had only the basemap in
the unit around home--it consistently showed a ring with about a
1000 ft radius. Does the unit use the installed map to help
determine position, or is the uncertainty in this case being
attributed to the map somehow due to its lack of detail?

--

Yes, it does use the detail of the map to decide the size of the
uncertainty ring. Back in the old days when I drove with my Garmin V
with only 19MB for detailed maps, I used to see this a lot outside the
detailed map area.

On Sat, 24 Jul 2010 14:48:50 -0700 (PDT),


Okay, thanks for the confirmation. I hadn't recalled seeing it
much before, so it kind of surprised me.

--

I don't agree with that. The only thing the program knows is where the
satellite signals think you are. The Accuracy is determined by the signal
levels and changes in satellite signal stability. You probably had weak
satellite signals or few satellites in range.

TheDuck wrote:
Actually, the satellites don't do any work/calculating they
only send signals, and the Receiver does the position
calculations. The rest of your premise is reasonably accurate.

Clay