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 5835-00-286-5432
NSN 6610-00-734-5976
NSN 5895-01-258-5933
NSN 5975-01-243-6831
NSN 5920-01-423-0805
NSN 4140-00-204-3563
NSN 6105-01-459-8823
NSN 5930-00-126-6670
NSN 5975-00-809-1000
NSN 5930-00-343-3743
NSN 5855-01-468-4996
NSN 5915-01-551-0745