The Model 4 has all photography functions on the front panel. These include the on/off power switch, discharge switch, Hi-Low frequency switch and variable frequency control. The discharge plate is located on the left hand side of the device. The terms discharge plate and film plate mean one and the same. The on/off switch provides main power to the circuit. discharge switch is a momentary contact switch that applies the electrical power to the discharge plate. The frequency control varies the frequency of the electrical power going to the discharge plate. When exposing sheet film and paper the device needs to operated in a photographic darkroom.