I’m a bit confused about the calculation for measuring the thickness of thrust bearing pads; could you please help me out?

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The last edit to this post was made by we11we11 on 2018-8-2 at 15:57. I came across a manual on Kingsbury-type point-contact tilting pad thrust bearings online, which mentioned the following method for measuring the thickness of the thrust pads: Measuring the thickness of the pads: Preparation: a flat surface, a set of dial indicators, and shims. Steps: 1. Place the flat surface on a stable surface, gently place the removed pad’s bearing surface on it, and position the dial indicator on the surface as shown in the diagram. 2. Measure the spherical shimming area, slide the sliding pad, and record the highest reading a. 3. Measure the readings for the eight tiles under positive and negative thrust in sequence and record them. 4. Then, combine a set of plug blocks h with similar heights, and similarly take measurements and record values b as the basis for calculation. 5. The actual thickness of the tile = h + (a – b), and record this value. I would like to ask: In step 2, the dial indicator is used to measure the reading at the highest point, which is denoted as a. The dial indicator can only determine relative heights; this value represents the relative height difference of the tile’s thickness. Another reading, b, is obtained using the same instrument and represents the relative height difference of the plug’s thickness. The actual thickness of the tile should be equal to h + (a – b). So how is it that the difference between these two thicknesses plus the thickness of the plug gives the actual thickness of the tile? I don’t understand; could everyone please tell me how the thickness is calculated?