Position sensors give input to the computer about the location of a moving part by varying the resistance in an electrical circuit. The computer sends a reference current through a circuit (made by a contact needle). The contact needle pivots over a resistor wire known as a "zigzag" wire. When the moving part moves, the needle goes to the left or the right. This alters the circuit's resistance which then changes the current returning to the computer. For example: when the needle moves to the left, the current goes through more of the resistor. The return flow decreases proportionately.