A system includes a longitudinal rack storing a plurality of items, a shoe movably attached to the rack, a magnet coupled to the shoe and a longitudinal circuit board arranged along the length of the rack. The circuit board includes an array of sensors along the length of the rack. Each sensor generates a voltage value depending on a position of the magnet in relation to the sensor. The circuit board further includes a memory storing voltage values generated by the sensors, and a processor configured to monitor voltage values generated by the sensors, detect that a particular sensor has generated a maximum voltage value and determine a number of items stored in the rack based at least in part upon a particular number of items corresponding to the particular sensor.