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 5975-00-625-8155
NSN 5990-01-443-2931
NSN 2925-01-462-1620
NSN 6220-01-530-5589
NSN 5835-01-368-4015
NSN 6610-01-608-2899
NSN 5985-00-270-0094
NSN 5895-00-548-9329
NSN 5905-01-434-5704
NSN 5855-01-395-0676
NSN 6135-00-276-7625
NSN 5930-01-524-5962