The method includes positioning a mask-frame assembly in predetermined spaced relation with the inner surface of a faceplate of a cathode-ray tube by means of at least four retractable spacing units. The spacing units are each extended a predetermined fixed distance, and the mask-frame assembly is mounted in the panel. Then the spacing units are retracted to allow the mask to be self-supporting in the panel, and the spacing between the mask and the face-plate is measured at discrete positions without removing the retracted spacing units.