The traditional Telegraph key (Morse key) is a spring-loaded rocker arm, swinging in a vertical plane, mounted on a fairly stable base. By pressing the end of the rocker arm, the operator closes the only electrical contact. Spring tension and rocker stroke (contact group gap) are adjustable to ensure comfortable operation for the operator. Less common are specimens with a horizontal movement of the rocker arm. There are keys in which the contacts work at the same time and the closure and opening of the circuit.