ultred ragnusen explained on 18/02/2018 :
And I can visualize how to mechanically clamp a bolt in a vise to hang the
torque wrench on - but then - how do you calibrate the two types?

I can imagine, when building them that they simply check the
calibration on a pass / fail basis. The only way I can think to adjust
them is via shims under the spring, to increase the tension.