A method for performing a load-on-demand operation on assigned graphic objects allows a user to load a computer file without the assigned graphic objects to shorten the loading time of the computer file. A list of locations such as logic gates and signal lines within the circuit where a fault is likely to occur is prepared. The internal movable body is connected to the outer hollow housing by means of a retainer key. The external casing rim and the outer edge of the cover plate are welded together, the thickness of the external casing at the rim is made small. The mating portion may receive the mating end of the electrically conductive contact.