All speedometers are regulated into slight plus from the wheel speed. This ensures you are not speeding unaware of it. Aside from the calibration issue, GPS ha

All speedometers are regulated into slight plus from the wheel speed. This ensures you are not speeding unaware of it. Aside from the calibration issue, GPS has poor or no coverage in tunnels, underpasses, mountainous areas and between dense urban high rises. Prone to EM interference too. Not a good thing for safety critical device.