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 2925-01-633-4048
NSN 5990-00-644-3365
NSN 2925-00-829-5124
NSN 5835-01-455-3380
NSN 5985-01-238-3899
NSN 5930-01-187-9251
NSN 5990-01-607-3528
NSN 5910-01-281-1818
NSN 6650-00-809-1817
NSN 5999-01-546-1305
NSN 5835-01-442-6482
NSN 6110-00-271-9928