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 5950-00-200-1110
NSN 6685-00-468-4223
NSN 6685-01-372-6010
NSN 5935-01-169-2656
NSN 2925-01-113-6904
NSN 2925-01-455-2558
NSN 5855-00-237-4088
NSN 6645-01-258-0370
NSN 5998-00-589-3719
NSN 5998-01-270-9192
NSN 5950-01-625-8829
NSN 5960-00-295-5413