I recently acquired a used Elcometer 345 digital coating thickness gauge, and calibration "shims" for 0.5 mils and 1.0 mils. These things aren't cheap. $425.00 on ebay.
The problem with measuring an increase in diameter after anodizing, and than dividing the increase by 2 for the thickness, is that for Type II, 1/3 of the anodize is below the surface, and the other 2/3 rds. is above the surface. For Type III, it's about 1/2 above and 1/2 below.
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