A switching assembly is disclosed for a high voltage aircraft ignition system. The device comprises: a generally rectangular box, a hinge, a generally rectangular lid, a locking means, and a power cord. The imaging areas of the zero-order light and one of the +1st-order diffracted light and the \u22121st-order diffracted light that is diffracted by the diffraction element do not overlap on the image pickup surface of the image pickup apparatus. The sample is classified in the class which has the associated weighted summation which is greatest in value.