This book astounds me. The depths they went to achieve millionth of inch accuracy was crazy. That book is quite expensive and rare it seems. I have a copy but it was 100$+ dollars.

There are a couple guys on YouTube doing very nice demonstrations of high-accuracy operations. One is Ox Tool Company. Interesting grinding operations etc.

Really smart stuff. These machinists of the 1930 1940 1950s were just as clever as John Carmack or whoever your modern nerd heroes are.