The technique for measuring crack thickness during certification
of specimens is selected according to whether the specimens are used to verify the performance
of flaw-detecting materials or to estimate the sensitivity of the testing. In either case, crack thickness is measured
on unpolluted specimens (i.e., without revealing cracks using the penetrant-dye or another method) with a Neofot, Polyvar Met, or other metallographic microscope with a magnification of 1500–2000
×
.