These are standard panels prepared by applying white emulsion paints on black scrub test panels. The films are indefinitely stable and the panels of each type essentially identical. They are used as controls in the measurement of scrub resistance, to obtain Calibration Ratings that normalize the wide variations often encountered for undefined reasons, among laboratories using the same scrub method. The Calibration Rating is the performance of the test paint panel expressed as a percentage relative to that of the selected Calibration Panel.