1. An apparatus comprising: a target device attached to and positioned above a first structure generating a target that is directed towards an imaging device; an imaging device attached to and positioned above a second structure, the second structure rotatably connected to the first structure by a hinged interface along a pivot axis; a plurality of images generated by the imaging device as the first structure is rotated relative to the second structure about the pivot axis, each of the plurality of images including a point object formed by the target; a calibrator, implemented by a computer system connected to the imaging device, that identifies a location difference of the point object in the plurality of images, identifies a plurality of rotation angles of the target relative to the imaging device based on a location difference of the point object in the plurality of images, identifies calibration information using the plurality of rotation angles, and uses the calibration information to calibrate a set of transducers by converting output data into angular data in angular units, the output data generated by the set of transducers configured to measure an amount of rotation of the first structure about the pivot axis when the first structure is rotated about the pivot axis relative to the second structure; wherein the target device is a light pen or other means for generating a light beam that is attached to the first structure and the target is a beam of light generated by the light pen or the other means for generating the light beam.