The cover glass is supported on these shoulders and leaves a depth of 0.1mm between the underside of the cover glass and the rectangle. The rectangle and the cover glass have optically plane surfaces. To facilitate calibration of the microscope, the rectangle has two engraved parallel lines spaced 1.382mm apart.

An accessory eyepiece micrometer is available which is ruled into squares, each of which is equal to 1/6 of the diameter of the eyepiece diaphragm opening. For mold counting, the microscope must give an area of 1.5 sq. mm (circle 1.382 mm in diameter) at magnification of 90-125.