working in the trade our guys have high end air guns but they still check with a proper torque wrench, wouldnt trust an air gun anyway all our torque wrenches are numbered/ calibrated/checked by an outside company every 6 months, they DONT calibrate air guns. You are more in danger of over tightening than under tightening we have 3 BMWs here that have had nuts 'gunned up' we are still trying to remove them, and yes we have all the high tech kit to do it but still struggling...