I feel like a couple of different questions are being raised here. My perception is that his method isn’t trying to “tune” a plate, so much as answer the question, “Where do I need to remove something?” He’s pursuing a goal of thinning the plate in a particular way, such that when the sound of rubbing or scratching or tapping is the same everywhere, he’s reached the goal. Such a plate would have slightly different thicknesses in various places, because the wood is slightly denser here, slightly less dense there. I think his method is rather elegant. One could, of course, simply measure the thickness with a dial caliper, but what thickness are we looking for? Of course that’s where we look at maps of plate thicknesses and follow them, but that doesn’t take into account variations in the wood. Maybe I’m completely wrong, but this is what it seems like to me.