Lehle Active Volume Pedal With Magnetic SensorThe Lehle Mono Volume is a volume pedal equipped with a precise magnetic sensor enabling it to operate almost wear free. This sensor uses the Hall effect, named after Edwin Hall, to measure the strength of magnetic fields. In the Lehle Mono Volume the Hall sensor, which is made in Germany, is accurately calibrated to the built in magnet and the control range of the pedal. The pedal moves only the magnet, the distance is measured by the Hall sensor