-Ta-Da! Operational, but not entirely finished, 1st thorough check of the plate's flatness (or rather the magnitude and locations of its deviations from "perfectly flat") shows that it is within the "AA Grade" specs*: less than 1,38 thousand of a mm. Not really surprised as my previous rough "Frying Pan Spherometer" already proved that - but rather amazed that it took me around 20 hours to make this instrument, but only 15 minutes to use it for checking this odd, anonymous plate. But then - I feel no regrets, as the tool (sans meter) would cost me 1600 bucks (+ postage...), and a plate of this grade would cost me another 400 plus shipping (just a bi-annual official inspection/ certification of this very plate would set me back 250 + shipping to and fro). Now I have it all for free, and I had some "hard fun" while making it (boldly copying some solutions from YouTubers OxTools, Matthew Tinker, NYC CNC & Catalina Racing in the conception). Zeroing the meter is real easy by using the diff screw (see elsewhere in folder) - instead of the original's crude wheel and coarse thread. My long measuring arm solution has a larger pivot radius than the original rough saw cut hinge/ flexure with the weird side arms for some "Band-Aid" yield point protection. Also - the black acrylic handle won't transfer my hand's heat into the instrument either (any heat differential IS an issue within the micrometer range), instead of the steel "butcher hooks" of the Rahn design. *US Federal Specification GGG-P-463c: AA: <1,38mu, A:<2,76mu, and B Grade: <5,52 mu for this odd-ball sized plate, though it really should've had almost another inch of thickness to fully comply with the AA standard - but the things I'll measure on it won't get this slab to buckle. //Unfortunately I have no plans, as I merely "winged it" on the go with available junk pieces. BUT - There's som more info/ rants on my design considerations and a few dimensions right here: https://www.homemadetools.net/forum/repeat-reading-gage-diyswedes-cheap-o-meter-73022