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

A way of manufacturing a precision device is created then other devices using a similar mechanism can be calibrated. A device is made that derives it’s calibration from some universal element. Another device is then calibrated against this. If the original device is inaccurate then sometimes the error can he calculated very accurately or the average of a number of readings from a number of devices are taken.

Answer 2

A way of manufacturing a precision device is created then other devices using a similar mechanism can be calibrated. A device is made that derives it’s calibration from some universal element. Another device is then calibrated against this. If the original device is inaccurate then sometimes the error can he calculated very accurately or the average of a number of readings from a number of devices are taken.