Lehle Mono Volume 90The Lehle Mono Volume 90 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 90, 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