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 5985-00-212-7690
NSN 5990-01-423-8189
NSN 5950-01-024-9461
NSN 6320-01-322-1310
NSN 6110-00-165-1528
NSN 6240-01-476-1612
NSN 5999-00-456-4819
NSN 5965-00-680-9749
NSN 5950-01-180-1357
NSN 5835-01-123-8305
NSN 7035-01-287-9817
NSN 5920-01-519-5550