How old is your torque wrench? Has it ever been left sitting with tension on the spring? Tools like torque wrenches and micrometers must be checked and recalibrated periodically to ensure accuracy. We suggest sending them back to the manufacturer, or you can do what we do and take them to your local aircraft maintenance facility. Aircraft mechanics are required to have these types of tools recalibrated each year, so they'll know where to send them and the cost is usually reasonable.