The pickup coil consists of a Hall effect sensor, which is housed within a metal rotor mounted on top of the distributor shaft. This shaft rotates by means of a gear driven by the camshaft. The rotor incorporates windows that open into a small space between the rotor and a stationary permanent magnet. The number of windows correlates with the number of cylinders in the engine. As the rotor spins, the windows pass in front of the sensor, exposing the magnet that triggers a signal to the car’s ignition system, which then fires a spark within firing order.