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 27 Instruments and apparatus for physical or chemical analysis (for example, polari 90 27 81 Mass spectrometers 90 27 81 00 Mass spectrometers Commodity Code Description 90 27 81 00 00 Mass spectrometers