a rotor is fixed to a steering shaft to rotate with the steering shaft , and outer and inner slits are formed along different circles on the rotor . outer and inner sensors , which detect the presence or absence of the slits , generate reflective codes and are located next to the rotor . stored pattern data that matches the reflective code is used to determine the rotational angle . alternatively , if the pattern data does not match the reflective codes , the rotational angle of the steering shaft is computed on the basis of the reflective codes .