Yep, I think I'll have to admit that you say a true thing here. It is only a possibility at this time.

In principe a normal GPS without S.A. degrading should be able to pin-point your position to within a radius of 3 to 5 meters. And thus compete closely with Differential GPS applications. In my last test I got accuracy of about 15 meter radius over a time span of 10 minutes; with a swing speed of 14.5 km./h at one time and about 9 km/h at another time. This is pretty drastic and I hadn't seen that before.

But yes there can be other reasons as well. The view of the sky in the test was not perfect and maybe the losing of 1 or 2 satellates shortly after one another could also have caused this rapid swings. Typically these are not present when on the water as there you have a prefect 360 degree sky and often I get signals of 5 satellites or more. This really helps.

Will try to do more tests when I have spare time; this time in an open plane and for longer periods of time

Wouter