If you didn't use the 5 foot radius on the spot lock your I-pilot would sit there and continuously turn left, right, left, right, etc trying to hold you that close to a certain spot. It never would be constant unless you were in a riverine environment where the current was smooth and steady. On a lake the wind is constantly changing and waves from boats don't help either. I think I would burn up the I-pilot steering pretty fast...

I believe the Humminbird 50 channel satellite GPS can stay on 2 foot accuracy very well.

DoubleG