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 6110-01-139-4646
NSN 4140-00-981-8580
NSN 5996-01-012-5716
NSN 5915-01-482-9620
NSN 5895-01-133-3585
NSN 5975-00-233-6301
NSN 6650-01-549-8478
NSN 5985-01-477-1256
NSN 6685-00-462-1009
NSN 6150-01-512-2976
NSN 5960-01-212-1626
NSN 6650-01-633-9147