I am interested in purchasing a GPS for my bike. I've looked at the Garmin 500 and it seems to do a lot of the things I want - speed, cadence, %grade, etc. But, I have a terrible sense of direction and hate to be lost. I need something that will not only allow me to map a ride but will also show me how to get back to the starting point on an "unmapped" ride. Does that make sense? Will the Garmin 500 do that? Is there something else that I should look into to?