I’ve got a new Garmin ETrex 3 which I’m really impressed with. I have noticed one anomaly though. On occasion, when the unit is static it does register movement for a few seconds. I haven’t have a chance to take it out on the bike yet, so these observations have been indoors with variable satellite reception and a variety of things might be affecting reception and positioning.

I just wondered whether this is anything to worry about; I believe that some drift is normal as, even with perfect reception, an absolutely precise position isn’t held (the Garmin website lists a range of effects that can degrade accuracy).

Completely normal.

That used to be caused by the random error that the US built into the civilian system to deliberately degrade the accuracy slightly.

What rockhopper is talking about is called selective availability, it have 100 or so meter offsets in position, but it was switched off a while ago- what you are seeing especially indoors is the effects of multi-path on the signals most likely. But don’t worry, Tis completely normal.

That used to be caused by the random error that the US built into the civilian system to deliberately degrade the accuracy slightly.

Turned off 14 years ago…

Unless you get a Differential GPS, or a Military P code set, all GPS units will show some movement.

Since SA was switched off you can expect about 5 – 10 m accuracy.

Check the “HDOP” and “VDOP” values, the lower the DOP the better the precision. HDOp is the more important.

DOPs

If you are sad like me then you may find this interesting GPS errors

I used to sell GPS but that was 20 years ago now! I didn’t know SA had been turned off.

Thanks for the info. it’s good to know that it’s not faulty; it’s a fantastic piece of kit for the money and it’ll take a while to get to know.

That used to be caused by the random error that the US built into the civilian system to deliberately degrade the accuracy slightly.
Turned off 14 years ago…

think it was bill clinton. we should thank or maybe monica lewinski 😉