Prepare the sample by cleaning the surface with a piece of emery paper or steel wool. The sample should be at least as smooth as can be obtained using size 400-A emery paper. The sample, if small, must be placed on a heavy, smooth, hard surface when the indentation is made. This is to overcome a lack of mass in thin sections.
Sheet metals to be measured should be at least 0.020 (0.5 mm) thick A smooth, hard metal surface must back up the sample. If the sample and the backing plate are not in contact, an erroneous reading will result.
Hold the indenter in the hand at right angles to the surface of the sample. Slowly force the tip into the sample until the indenter trips. A clean, smooth, shallow cavity will result.
Twist the barrel of the flashlight until the light comes on so that the base is illuminated. Place the microscope over the sample so that the hole in the microscope base is over the indentation. Center the indentation in the sight so that the reticle is tangential to the indentation.
The hardness may now be obtained by measuring the diameter of the indentation with the scale in the microscope. The values are in equivalent Rockwell C Scale. Several measurements should be made as the sample being tested may have soft or hard spots.