So I'm looking into how stuff is made from scratch, starting with a surface plate which has been lapped flat using the three plate method. But almost everything I read on the subject on "the history of precision" and such stops there and glosses over the rest by simply stating that it's possible. How does one go about making perfect 90 degree corners from simply a flat surface?
To clarify, when I say "from scratch" I mean going from no tools at all to a perfectly square block. I'm asking about the history of machining, how the first precision machines were made.
If anyone has any good resources on the subject which explains it in further detail I would appreciate it very much :)