A pointing device that consists of a ball supported on bearings so that it is free to rotate in any direction but is restrained within a socket so that less than half of its surface is exposed. In use, the ball is rotated by the operator’s fingers and sensors on two of the support bearings generate trains of pulses related to the rotation of the ball about two axes at right angles. In the late 1970s such devices were expensive and were only used in applications such as air traffic control; by the mid-1980s they had reduced significantly in price and become popular for personal computer applications. Laptop and notebook computers often incorporated trackerballs into their keyboards. Their use has declined with the advent of touchpads and other input devices that are less sensitive to ingress of dirt.