Have one in my machine shop AJAWAM Swarf Page
… seems to help.
I have a dial guage that I can use for this. Lately though, I simply print 20mm X 20mm 1-layer squares in the corners & center. This guarantees me that I’m not only level, but I’m getting the texture & line adhesion I’m looking for. Plus, it uses very little filament, and accounts for slight differences between spools of filament.
I guess we are all sort of gadget men trying to master our possibilities in 3d printing. Maybe if I had many printers ideas like this might help but bed levelling has not been a real problem with one Ender 3 pro. When I see the problems that people have with automatic bed levelling that turned me right off even though I love the idea of “control” especially with a technology that boggled my ancient mind at first.