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SCIENTIFIC INSTRUMENTS-NAMELY, CATHETOMETERS, [ CHRONOGRAPHS ], COLLIMATORS, COMPARATORS, COMPENSATORS, CREEP TEST EQUIPMENT, DIAPHRAGMS, DILATOMETERS, [ DIVIDING MACHINES, ECHELONS ], ELLIPSOMETERS, FILTERS, [ HELIOSTATS ], INTERFERENCE APPARATUS, INTERFEROMETERS, LABORATORY SUPPORTS, LENSES AND EYEPIECES, LEVELS AND LEVEL TESTERS, LIGHT SOURCES AND ILLUMINATORS, [ METER BARS ], MICROMETERS, MICROSCOPES, MIRRORS, MONOCHROMATORS, OBJECT HOLDERS, OPTICAL BENCHES, CARRIAGES, SLIDES, AND ACCESSORIES, OPTICAL VIBRATION MEASURING EQUIPMENT, PHOTOMETERS, POLARISCOPES, PRECISION LINEAR SCALES, REFRACTOMETERS, SCREENS, SLIDES, SLITS, SPECTROGRAPHS, [ SPECTROMETERS ], SPECTROSCOPES, SPHEROMETERS, [ SPECTRUM TUBES ], TELESCOPES, THERMAL EXPANSION INSTRUMENTS, THERMOMETERS, AND BURETTE READERS, [ THERMOPILES, TIME MARKERS, VISCOMETERS ], WAVE PLATES, SUPPORTS, STANDS, CLAMPS, HOLDERS, ADAPTORS, ADJUSTING PLATES, AND EQUIPMENT THEREFOR