initiate the teach cycle in the present invention the power wires are the blue wire and the black wire so the power terminals for providing power to the sensing device 10 are terminals 75 and 74 terminals 71 53 are connected to the potentiometer 40 and are used in conjunction with the control box 70 to measure the voltage across the potentiometer 40 when the sensing arm 34 is in contact with the object whose position is to be monitored accordingly the system using the sensing device 10 works in conjunction with the control unit 70 as follows first a teach in procedure is conducted in which the d c motor 20 is actuated for a predetermined time and the sensor arm 34 is swung into contact with the tool 60 both shafts 23 and 22 turn as a result of actuation of the d c motor 20 when shaft 23 coupled to sensing arm 34 swings the sensing arm 34 to a stopped position shaft 22 also moves in a manner that is equal to although it could also be proportional to the movement of shaft 23 shaft 22 is coupled to the potentiometer shaft 42 turning shaft 22 turns shaft 42 of the potentiometer 40 resulting in a change of the voltage level across the potentiometer 40 when the sensing arm 34 is swung from its starting position and contacts the tool 60 the voltage produced across the potentiometer 40 at this point is measured and recorded since this voltage which changes.