Thread: About 37xx converted to 34xx satellites reception accuracy

When I did the conversion I used 3490 3.60 firmware.
I have the common poor accurany problem when watching the satellite screen, but in "real life" I've never encountered any "real" problem.
The satellite bars jump up and down, but I've never had the car jumping to another nearby street, even when I was stationery at a traffic light.

So I've decided to do a different kind of test to check my converted 3760>3490
As I was walking to work today, the sky was 100% clear and I had a perfect view north, east and south with no buildings at all.
On my west side I had 7-story buildings.
I stopped at a corner, got a satellite fix and in seconds it went from ~60m down to 15m accuracy.
Then I turned on Diagnostic Logging Recording (1 point every one second) and here are the results in "real life"
During the 3:40 minutes of the recording, I was standing still at the place on the pavement (blue dot) and keeping time with my phone's timer to check the results later.


1) Accuracy 16~15 m
I seperated the first 40 seconds of the recording and I was surprised to see in Mapsource that even with 15m accuracy, the gpx was indicating my real position.
I could not believe that those 40 gpx points where so close together, almost at the same point, all of them almost at my real position.



2) Accuracy 12~6 m
After those first 40 secconds the accuracy became better and better very fast, and settled down to a stable 6 m.
After 3 minutes (at 6 m most of the time, and never more than 8 m) I turned off the recording.
Back at Mapsource I was again surprised to see that, with better accuracy, my position was not indicated as good as it was above.
Now the 3490 signal was moving around a "box" 11x16 meters.
But even this I find it as very good reception, 180 gpx points, so close together and so close to my real position and for so long (~3 minutes)!!!



From all the above I think that my converted 3760 is very accurate in "real life", even if the indicated accuracy is around 20 or 15 or 10 meters.
My position was correctly indicated in relation with the gpx file I've got.
Accuracy in meters is a probable margin of error in the gps signal.
What I've showed above is that even with "poor" accuracy, the "real" gps fix (recorded gpx points) is extermly close to my real potition.
Accuracy of 15m doesn't necessary means that 3490 indicates my position 15 meters away from the real one.
It means that my real position "could be" within a circle of 15m radius of the gps fix.
The good thing is that, even I was standing still at the same position, the actual points-fixes that 3490 was recording, were very-very close to my real position most of the time, no matter how poor my accuracy was, or how big the blue circle on the screen was.
I don't think that there is a real problem with the gps fix, I think there is a problem with the mathematical calculation of accuracy.

It would be very interesting to have one 3790 and one converted 3490 side-by-side doing Diagnosting Logging for some time.
Then we would compare their gpx files.
What would we say if a 3790 with 4m accuracy and a 3490 with 20m accuracy, at the same place, same time and same weather, gave very similar gpx files...
If both devices gave gpx points very close to our real potition, then "maybe" accuracy is not so important if the "real" fix is always very close to our "real" position.