Re: What's your average speed?
Yup... the GPS can read a mph or 2 sometimes just sitting there, but you can compare it's readings once moving by putting it in your car and comparing with the car's speedo as most late model cars are pretty accurate. Probably the most accurate way to check speed is by radar readings, but then ya need a radar gun and either a second person to record the readings or a tripod and an open stretch where you could run the same distance in both directions then average out the results if different.
Some of the aftermarket gauge companies are making GPS speedometers for cars and motorcycles with much faster sampling rates so the analog needle moves up smoothly and as quickly as a mechanical unit during acceleration. These are really nice for custom hot rods since there's just 2 or 3 wires to connect... the battery, the ground, and the backlighting. They're still kinda expensive now, but the price should come down as they catch on.