A method, system, and computer program product for identifying invalid memory references. The controller further controls the laser emitting element to irradiate the laser beam in a reduced light amount every at least one line. In addition, the N-port automatic calibration device comprises at least one single-pole, double-throw switch, having a single-pole coupled to a second port of the N-ports of the automatic calibration device, having a first throw coupled to a first load impedance, and having a second throw coupled to a throw of the N1 throws of the single-pole, N1 throw switch.