Section 18 OPTICAL, PHOTOGRAPHIC, CINEMATOGRAPHIC, MEASURING, CHECKING, PRECISION , MEDICAL OR SURGICAL INSTRUMENTS AND APPARATUS; CLOCKS AND WATCHES; M USICAL INSTRUMENTS; PARTS AND ACCESSORIES THEREOF 90 Optical, photographic, cinematographic measuring, checking, precision, medical o 90 20 Other breathing appliances and gas masks, excluding protective masks having neit 90 20 00 90 20 00 00 Commodity Code Description 90 20 00 00 00 Other breathing appliances and gas masks, excluding protective masks having neither mech