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

WRT torque, torque is defined as a force at a given distance from a rotation point

So 20 ft-lbs is equivalent to hanging a 20 lb weight 1 ft away from the rotation point, assuming a massless bar doing the connection. So you need a way to account for the mass of the metal bar that you use to connect the weight and the rotation point.