ELI5, How are precision calibration tools, themselves calibrated?

Question

Feels like a chicken and egg senario. Let’s say I get my torque wrench from work sent off to be calibrated, and that’s calibrated with something itself needs to be calibrated, and so on and so fourth. How’s that figured out?

In: 430

Answer 1

With something like a torque wrench, you can calibrate it with an ordinary scale/balance. Multiply the force applied to the wrench by the length of the lever arm to get the torque, then compare that to the setting on the wrench. Don’t forget to account for the torque from weight of the wrench itself.

Answer 2

With something like a torque wrench, you can calibrate it with an ordinary scale/balance. Multiply the force applied to the wrench by the length of the lever arm to get the torque, then compare that to the setting on the wrench. Don’t forget to account for the torque from weight of the wrench itself.