A mechanical system for selectively moving a load a motive distance comprises an actuator operable for applying a force to the load. Synchronized with the rotation of the first display plate, the LEDs in the light emission part light on and off to display symbols or images by utilizing afterimage effect. The microprocessor generates an activation control signal of a liquid crystal activating portion, a driving control signal of a liquid crystal driving portion, and a power off control signal in response to a simultaneous detection of a welding light and a high frequency generated during a welding process.