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 4140-01-160-5109
NSN 6320-00-925-0558
NSN 6320-00-521-9350
NSN 5960-00-099-9790
NSN 5999-01-417-2033
NSN 5960-00-151-7576
NSN 5925-00-217-6381
NSN 5945-01-174-3457
NSN 5920-01-550-9545
NSN 6620-00-935-1321
NSN 7035-01-531-0468
NSN 5960-01-478-8546