While it's true that torque wrenches do require calibrating - not every torque wrench can be adjusted. If you think that yours is seriously wrong (and it can be adjusted) then you have a couple of options. Most busy garages get their torque wrenches calibrated every year or so. There are companies that you can send your item to that will calibrate it for you - these cost around £30-50 (not including postage). So you'll need to work out if you think your wrench really does need calibrating and whether or not you'd like to have it calibrated or just replace it. Of course, you can calibrate your torque wrench at home using a vice, a good quality/correct weight, some cord and some maths - this is probably the best route for most DIYers.