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 6240-00-732-0496
NSN 6240-01-279-0552
NSN 6240-01-502-7280
NSN 5920-00-676-9113
NSN 5985-01-569-6740
NSN 5915-00-142-6912
NSN 5895-00-067-9058
NSN 5910-00-203-5373
NSN 5990-01-570-5471
NSN 6145-00-493-4073
NSN 5945-01-508-4228
NSN 6150-01-430-9512