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An instrument for indicating the distance traveled by a vehicle, typically by measuring the number of rotations of a wheel or fan whose rate of rotation depends on the speed of the vehicle. Compare speedometer.
The use of motion sensors to determine a robot's change in position relative to some known position. For example, if a robot is traveling in a straight line and if it knows the diameter of its wheels, then by counting the number of wheel revolutions it can determine how far it has traveled. Robots will often have shaft encoders attached to their drive wheels which emit a fixed number of pulses per revolution. By counting these pulses, the processor can estimate the distance traveled.