Unless something has changed lately, I don't think that GPS of any manufacturer is very good at speeds below about 3 MPH. It has to do with the timing available to civilians or something. I'm not sure. When looking for my unit for the boat, I read quite a bit and talked with several folks and that seemed to be the consensus... You won't get an accurate reading below 3MPH.

I'm still cussing under my breath over that one.