Section 18 Optical, photographic, cinematographic, measuring, checking, precision, medical or surgical instruments and apparatus; clocks and watches; musical instruments; parts and accessories thereof 90 Optical, photographic, cinematographic, measuring, checking, precision, medical or surgical instruments and apparatus; parts and accessories thereof 90 20 Other breathing appliances and gas masks, excluding protective masks having neither mechanical parts nor replaceable filters. Commodity Code Description 90 20 00 Ozone therapy, oxygen therapy, aerosol therapy, artificial respiration apparatus