The lamps' brightness was controllable with a variable resistor. A humistor is a type of variable resistor whose resistance varies based on humidity. The joystick potentiometer acted as a variable resistor in the RC network. A PIN diode, suitably biased, therefore acts as a variable resistor. The variable resistor is adjusted until the galvanometer reads zero. Other notable inventions include a variable resistor used in guided missiles. A variable resistor would dissipate power as heat and acts as a voltage divider.