A apparatus for sensing a surface of material in a storage container is provided. The apparatus comprises a housing, a motor assembly, a swing arm assembly, an optical assembly, a material surface detector, and an electronic control circuit. The motor assembly has a motor and a reel carrying a cable. The swing arm assembly has a swing arm with a magnet and a sensor circuit. The sensor circuit monitors a magnetic flux to determine a surface detector position. The optical assembly has a measuring wheel, a code wheel, and an optical encoder circuit. The optical encoder circuit monitors rotation of the code wheel. When the surface detector is moved between first and second positions based upon input from the sensor circuit, the control circuit receives input from the optical encoder circuit based on the rotation of the code wheel. As such, the surface of the material is sensed.