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 6220-00-397-6320
NSN 6320-01-089-9086
NSN 5950-00-060-4231
NSN 5895-01-181-5471
NSN 5996-00-338-4022
NSN 6650-00-933-8744
NSN 5835-00-264-0946
NSN 6240-01-401-5340
NSN 5950-01-564-7699
NSN 5945-01-535-1352
NSN 5975-00-290-4285
NSN 2925-01-649-7543