A method of incrementally reducing a design is disclosed. The transducer is pulsed with one of rectangular waves and tone pips of a selected frequency to emit pulsed audible sounds at predetermined times. More particularly, the distortion discrimination circuitry includes impulse noise circuitry that looks for high frequency noise in both the magnitude and multiplexed outputs of the demodulator to determine the occurrence of impulse noise distortion events. Any other portion of the thread of the bolt has a second minor diameter which is smaller than the first minor diameter.