A flat, transparent piece of glass, generally of fused quartz, with one or both principal surfaces polished to within a few millionths of an inch of a true plane. It is used in conjunction with a monochromatic light source to measure the flatness of precision finished surfaces, and to determine the distance and parallelism between precision finished surfaces by comparison with known standards. In operation the flat is superimposed, reference surface downward, on the parts under test and when illuminated by monochromatic light the rays reflected from the reference surface are either reinforced or neutralized by the rays reflected from the surface under test producing interference bands which reveal any variations in the thickness of the film of air between surface under test and the flat. Excludes optical parallels.
NSN 5999-01-411-4298
NSN 5930-00-584-9313
NSN 5960-01-181-2143
NSN 6220-01-389-4792
NSN 5975-01-468-4962
NSN 5905-01-287-8450
NSN 5925-01-392-2860
NSN 6320-01-177-3192
NSN 5990-01-110-4841
NSN 5965-01-413-9205
NSN 5925-01-462-6172
NSN 5920-01-533-2602