Electric screwdriver accessories include a range of replacement parts and add-on components that enhance screwdriver performance. Digital and analog power units have LED outputs to display power, torque and error information. Analog units use knobs to adjust torque, speed and ramp values, while digital power units have a backlit digital display. Other accessories include spiral tool cables, balancers and torque testers. Spiral tool cables are highly flexible units that connect components without kinking. Balancers help control electric screwdrivers in vertical-down applications. Torque testers measure torque output to calibrate electric screwdrivers.