The coupling is the final positioning device and is solely responsible for maintaining that faceplate orientation in all planes. Each coupling is designed with the highest possible coupling lock force and largest diameter to achieve maximum rigidity. A. G. Davis Circle Divider® and AA Gage Ultradex® tables maintain their accuracy indefinitely without any adjustments. The accuracy actually improves through normal use. This occurs because teeth have a natural tendency to conform to size, shape and pitch.