A method includes: classifying sampling points into ranks so as to satisfy a condition such as a condition that no SP belonging to a certain rank is dominated by another SP belonging to a rank higher than the certain rank; determining, in ascending order from a lowest rank, whether a first SP belonging to a first rank dominates a second SP belonging to a second rank higher than the first rank. The drive roll release mechanism further includes an actuator in sliding communication with the carrier body. The engine of the boat can move vertically through moving a frame the engine mounted to by a motor where the propeller installed to the lowest end of a stem of the engine. A checker is provided for providing an indication of the information integrity in response to bits produced at an output of the FIFO in the predetermined bit location. The signal duty detecting apparatus includes: a level detector detecting levels of an input signal; a counter counting the levels detected by the level detector; and a duty calculator calculating a duty of the input signal based on the levels counted by the counter.