Optical Surface Quality: What Do 40-20 and 60-40 Mean?
Scratch-dig surface quality describes limits on visible imperfections in an optical surface. Under the MIL-PRF-13830B convention, 40-20 means a scratch comparison grade of 40 and a maximum dig diameter of 0.20 mm; 60-40 means grade 60 and 0.40 mm. Lower numbers set tighter limits within the same inspection system. The scratch number is not a …
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