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I have no idea but as I too have a torque wrench was curious, I came across this it's on calibration so no idea if it's going to be of any help or not. I'm guessing not as I sure you did your own search, but anyway.
How to Calibrate a Torque Wrench: 10 Steps (with Pictures)
Unless properly calibrated by a certified calibration facility you might as well use a crescent wrench and "wrist calibration". At the weapons maintenance facility I worked at if a torque wrench was dropped it was taken out of service and had to be recalibrated.
While it is not calibration, I check the accuracy of my torque wrenches by "attaching" two together and verifying that they are getting abo9uyt the same result. Put a socket on one that will engage the square on the other and which "clicks" first. then play with the settings to see how close they are. Try it at various settings of the range you want to use.
If it is a "click and break" type there is a screw in the handle that could be misadjusted or broke. If it is a bar type it could be stressed from over work. The trick with a bar type is if you torque 50 clockwise when finished torque it 50 counter clockwise to keep the stress balanced.
I have a number of these, in ranges up to 1200 ft lbs.