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 6220-01-589-5154
NSN 6150-00-764-1943
NSN 6130-01-626-6540
NSN 5835-01-442-6482
NSN 6135-01-608-2355
NSN 6645-00-296-8310
NSN 6620-00-801-8885
NSN 5915-01-432-0324
NSN 7035-01-421-4446
NSN 4140-00-619-8062
NSN 5835-01-474-1224
NSN 5950-01-537-7577