PURPOSE: To increase the calculation accuracy as well as to reduce the measurement of the operator by providing the balanced beam containing the first arm lever which rotates co centering on the axle fulcrum and the second arm lever which is combined to the first arm lever which is combined to the first arm lever and whose other end is displaced on the reference line passing through the fulcrum and then performing a specified operation based on the angle which is formed by the both levers and the reference line plus the displaced position at the end part of the balanced beam.