A method is disclosed for calibrating the half-tone operation of a color marking engine for creating images formed in bi-level or quad-level dot density formats. The device provides a solar cell load circuit by connecting the solar cell with an electronic load device setting a load current or voltage variably, and a measurement circuit connecting voltage and current detectors with the load. The axial seating pin has a shank that slides into an aperture on the tool body and is then held to the body using a fastener.