jkirkebo wrote:I have verified that the average speed is the correct one, by external GPS and radar speed displays along the road.
GPS is only as accurate as its own current accuracy and sample rate. Roadside radar speed displays usually display low due to using older RADAR technolgy and their positioning/aim on the road. Systems like LIDAR that law enforcement use are much more accurate and would probably be better to test your speedometer. Know any cops?