GPS speedometers are used typically for fun, or as backup when their regular speedometers are not working. A GPS is capable of reading the speed of your vehicle by recording how far the receiver has moved since the last measurement was taken. The speedometer accuracy is thus based upon a moving average, subject to the quality of the current satellite signal on the road. For this reason, GPS speedometers are helpful, but not as accurate as car speedometers.
How to use a GPS as a Speedometer
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