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 6610-01-293-0644
NSN 5965-01-463-8176
NSN 5855-01-091-2273
NSN 6620-01-258-8980
NSN 6650-01-067-0132
NSN 5965-00-926-2591
NSN 6150-01-102-2446
NSN 5855-00-058-1293
NSN 6685-01-455-7373
NSN 5905-01-287-9405
NSN 5975-00-761-2834
NSN 5960-01-481-8051