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 5990-01-236-8399
NSN 6620-01-418-3245
NSN 5895-01-459-1394
NSN 5895-01-142-5765
NSN 4140-00-215-0313
NSN 6240-00-467-7295
NSN 5915-01-354-4729
NSN 5950-01-066-9148
NSN 5950-00-188-9141
NSN 6240-00-888-7563
NSN 6150-00-493-1840
NSN 6610-00-058-0900