eli5 How do precision tool manufacturers get their first calibrations

Question

I worked a lot with torque wrenches in the Army, and always wondered how the “first” torque wrench was calibrated without another one to verify that it was accurate? Was there another tool to verify the calibration was correct and if so how did that one get calibrated. In my head it keeps asking “well how did the next one get calibrated?” Every time I think about the first precision tools of any type, not just for torque.

In: 8

Answer 1

For a fascinating look into the history of precision, try The Perfectionists by Simon Winchester.