In this video we use the Marvel Saw to help make a cast iron lap and then precision lap a hardened Anton v block. We check the results of the lapping with a monochromatic light source and an optical flat.
Microgrit abrasives https://www.microgrit.com/index.html
Accu-finish/Glendo https://accu-finish.com/
Optical flats https://en.wikipedia.org/wiki/Optical_flat