Re:Hand Scraping a Truly Flat Plane (1908) [pdf]
by jbay on Friday April 17, 2020 @02:12AM
(#22896665)
Fast-forward to 2016 to see how much the technology has changed:
https://www.nist.gov/news-events/news/2016/09/meet-bob-pmls-...
Circa mid-1960s, this defined precision: https://www.amazon.com/Foundations-mechanical-accuracy-Wayne... (at this level of precision, you need a room-within-a-room climate control, because thermal expansion of objects). That leads down the rathole of "jig borers" for making precisely located holes of precise radius and diamond turning machines which are nice for cutting optics.