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 23 Instruments, apparatus and models, designed for demonstrational purposes (for ex 90 23 00 Commodity Code Description 90 23 00 00