The only one you can calibrate is the click type or dial. They don't do much with a beam style t-wrench either they are good or not. There is nothing wrong with a used t-wrench, I use them all the time. Find one that is not all beat up, and go for a good name one if you can find one. The thing with torque wrenches is they are only as accurate as you want them to be. If you take them in yearly for calibration, and never drop them, leave them in your jeep, they will over time go out of cal anyways, but faster if used and not stored properly. To check for a cal (cheep way )use 2 torgue wrenches and see if they match or how much they are out and deveide the difference and either add or substract the amount to the one that you want to use. If you can find a good name one I'd go go for that one over a cheeper one. Usually they are closer tolerence and will be more accurate, right out of the box. LBS/FT or LBS/IN is usually a preference, what do the manules that you are using give for mesurments? get that one, less math for you.