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 6650-00-205-6282
NSN 5975-01-033-4892
NSN 5945-01-179-4776
NSN 6220-00-512-9472
NSN 5920-01-359-1197
NSN 6650-01-024-9554
NSN 5965-01-600-0566
NSN 5990-01-414-0543
NSN 5945-00-979-5479
NSN 5855-01-507-7394
NSN 5910-01-317-5553
NSN 5925-01-411-6028