The Howard mold counting chamber is used for mold counts in tomato products including canned tomatoes, tomato soup, dehydrated tomato, canned spaghetti, pork and beans, and similar products containing tomato sauce.

In the center of the glass slide is a rectangle 15 x 20 mm, which is flanked by shoulders on each side 0.1mm higher.

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 square mm (circle 1.382 mm in diameter) at magnification of 90-125.