marshg246
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- Jul 12, 2015
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Each turn of the rear wheel turns the speedo cable inner an exact number of turns. Change the diameter of the tire and clearly you upset the cable turns count. The speedo head can be thought of a voltmeter - spin a magnet in a coil of wire and a voltage is produced - spin faster and more voltage is produced. Calibrate accurately and you'll have an accurate speed if the tire diameter is correct. They are only accurate at the speed calibrated but that's the same for most speedos.
Due to a bunch of factors, especially how many satellites captured, GPS is not always accurate. You must know the distance to at least two satellites and the speed of light to have any hope of speed accuracy and three gives flat-line accuracy in most cases while four allows altitude changes to be accounted for. And you must have fast enough hardware to do the calculations in real-time. Most of the time, you're simply averaging previous readings.
Due to a bunch of factors, especially how many satellites captured, GPS is not always accurate. You must know the distance to at least two satellites and the speed of light to have any hope of speed accuracy and three gives flat-line accuracy in most cases while four allows altitude changes to be accounted for. And you must have fast enough hardware to do the calculations in real-time. Most of the time, you're simply averaging previous readings.