It is noted that the volume state cannot be any case other than case D because, firstly, processing would not reach step S15-66 if volume state case A was detected at step S15-64, secondly, the value of counter np will be equal to 3 if volume state case B or C exists, and thirdly, the value of counter np will be greater than 3 if any of volume state cases D to H exists because of the processing pe