1. Steps Use a vernier caliper to measure the height of the steps, and measure the maximum value as the height of the steps.
2. The visible cracks are visually inspected, and the hidden cracks are determined by the hammering method (that is, hitting the plate with a metal hammer, and distinguishing whether there is a crack by sound, generally a mute sound).
3. Spots Use a vernier caliper to measure the size of the spots, and visually measure the number of spots.
