Quote:
Originally Posted by reformed
The portable GPS units are less accurate because they don't use the speed sense signal from the vehicle in their calculations like the in-dash ones do. Combining the actual speed sense signal with the GPS triangulation, makes them more accurate.
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I don't buy it... I'd hope in dash units with a speed sensor line use it to calibrate to the GPS network (or when GPS signal isn't available). In any case, that doesn't answer the question of why. Why would a GPS be less accurate? I mean, our airlines rely on the same exact satellites - the military relies on the same exact technology... Even large ships rely on it. And they don't have a direct reference to a stationary "ground."
GPS signals propagate at the speed of light - much faster than signals from a hall sensor.