The gauge cell is the only part that requires calibration. The gauge cell consists of the hydraulic load cell and gauge either analogue or digital. The gauge cell is attached to the tester base with two cap screws. Turn the capstan arms counter clockwise to lower the torque bar as much as possible for screw access. If you turn the tester upside down you will notice the screws through the top of the base. Remove these screws then thread the gauge cell off of the power screw. Sent the gauge cell for calibration. Gauge cells are interchangeable and replaceable. You may wish to keep a spare for emergencies.