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.
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We have created the units we use. As long as you have a definition that can be repeatably used to measure it you can use it to calibrate other devices. All of the units we use have been arbitrarily defined. So what is relevant is that everyone uses the same definition what the definition is.
Torque is rotational force over a distance messure in newton-meter or foot-pound. So you need to be able to measure the distance from the center of rotation and the force you apply there.
The distance is more obvious in how it works.
Force units have historically been based on the weight if a specific mass at the surface of the earth. Because the earth’s gravity is not exactly the same everywhere measuring it very accurately is a bit tricky to get very exact, the total variation on the surface of the earth is only 0.7%.
So a simple way to calibrate the to some degree of accuracy is to mount the horizontal and suspend a known weight at a know distance from the rotational center. The torque is easy to calculate. You can change the distance and/or weight to the correct torque and use it to calibrate the measurement part on the wrench.
A guess is a calibration like that can without a lot of problems be accurate to a few percent and will be the same as most torque wrenches
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