Norbar torque wrench calibration?

Hi all,

Random one for you. I recently acquired a norbar 4r torque wrench.. It was bent and needed the ratchet replacing, all of which I've dealt with. Using length x weight I can see it needs calibrating as it breaks about 15% early. I want to have a go myself, I can get an exploded diagram of the internals and there's a few washers which pretension the springs in the handle. I imagine you need to add more tension so it breaks later. Does anyone know the process? I've searched the web, but can't find any how to guide on calibrating commercial sized break back torque wrenches?
As always any help gratefully received! Cheers

I don't know either, but your plan sounds sensible. Did you lubricate it when you put it back together? I'd imagine that dry/oil/grease would give different results.

Thanks for response, I've lubricated the parts I'd worked on and they're all very smooth in operation, but I've not yet removed the adjusting hex nut which holds back the spring and washers.. I'm looking for a little reassurance that when I do, everything isn't going to come flying out etc!