Deck height

to get a piston recession value that is meaningful for use in claculations for compression
1) you must have the piston in the bore that is being measured at top dead center. The way to do that is with a piston stop. Install the stop, install a degree wheel, rotate the engine clockwise so the piston hits the stop, observe / mark the reading on the degree wheel. Rotate the crank counter clockwise, so the piston comes to the stop. Observe / mark the reading. Remove the piston stop and move the crank to the degree rerading exactly half way beteen the two. The piston where the stop was will be at TDC
2) a method to measure accurately,, depth micrometer, or block of known height, feeler gauges and a straight edge..

and yes, the poster is confusing a piston measurement, center of pin bore to top of piston ( compression height) with piston recession.