DIY measuring and lapping a worn surface plate

[DIYSwede]

-Anybody here on HMT using uncalibrated surface plates, worn for years with unknown flatness properties,
lacking the funding or willingness for transport, calibration and resurfacing by a certified techie?

-Anybody wondering why the professionals refuse to show how they lap worn plates back into spec?

-Anybody wanting to DIY the whole process down to the tolerances the techies won't reach,
as nobody wants to spend that kind of money?

-Anybody wanting an AA grade (w/o a 200 dollar sticker) plate, willing to waste 10-20 bucks and a few evenings of elbow grease?

Matthew Tinker has done it: Knocked together a DIY repeat gage, ordered some online diamond dust,
charged an old CI plate with it and started lapping a big granite plate himself.

Look for yourself as he's showing the entire process down to 1 micrometer of deviation: