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 5905-00-431-6202
NSN 5950-01-188-5846
NSN 6620-01-597-5013
NSN 6135-01-231-4809
NSN 5910-00-255-6228
NSN 5996-00-115-2932
NSN 2925-01-464-3093
NSN 5960-01-185-4216
NSN 6320-01-215-1133
NSN 5855-01-068-3683
NSN 5965-01-340-8968
NSN 6610-00-170-6715