Visual methods of measuring case depth have been classified into two general categories: macroscopic and microscopic. In macroscopic procedures, specimens normally are ground no finer than through No. 000 metal-lographic emery paper (600 grit silicon carbide paper), and magnifications usually do not exceed 20 diameters. The Brinell microscope, a hand-held optical instrument with reticle markings at intervals of 0.1 mm (about 0.004 in.) and 20 diameters magnification, is a convenient tool for macroscopic measurement.
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