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.
Quit complaining about the color, just pull up your skirt and fish! -- snagged