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 6135-01-492-5717
NSN 5990-00-221-0878
NSN 5925-01-458-0355
NSN 6610-00-060-0871
NSN 6240-00-406-1510
NSN 5920-01-449-4075
NSN 6110-00-659-3348
NSN 6645-00-145-6411
NSN 6650-01-502-6761
NSN 6240-00-423-9575
NSN 4140-00-445-3578
NSN 5945-01-014-7051