https://youtu.be/gNRnrn5DE58?si=VTrpcfDDDukItwCH
It’s an older video, but I really enjoyed it and found it really thought provoking. Precision is something we take for granted but as this video shows it’s something that was incredibly difficult to get to where we are.
Also, my metric crew rise up!! The inch is legally defined by the metric equivalent.
3-plate flatness method crew unite!
I find it interesting that our current definition of the inch is based on an industrial standard that had been in use for decades. And that that standard was, in effect, created by one man.
tldr: Carl Edvard Johansson was a Swedish manufacturer of gauge blocks who built his one-inch blocks by ignoring the differences between the UK standard inch and the US standard inch. Those standards were only a few millionths of an “inch” (pick one!) apart anyway, so throwing away most of the decimal places must have seemed like a good idea.