an instrument used in motor vehicles to measure the speed of travel and the distance traveled. The speed indicator of a speedometer is magnetically operated, and the distance counter (odometer) operates mechanically by means of rollers. In mechanically driven speedometers, both the speed indicator and the odometer are connected by means of a flexible cable to a set of reduction gears, one gear of which is driven from the driven shaft of the vehicle’s transmission. In electrically driven speedometers, the transmission’s driven shaft is connected to a contact breaker that functions as a pickup and converts direct current into three-phase alternating current. The frequency of the alternating current is proportional to the speed of rotation of the driven shaft. The current feeds an electric motor, whose rotor rotates at the same speed as that of the pickup.