Trackball

A trackball is a pointing device consisting of an exposed ball held in a socket, with sensors that detect the ball's rotation about two axes as the user rolls it with a thumb, fingers or the palm of the hand, pressing separate buttons with the fingertips; unlike a mouse, which must be lifted and repositioned, a trackball only requires lifting the finger or hand from the ball itself, and many models have low enough friction that the ball will keep spinning once set in motion. The British Royal Navy Scientific Service engineer Ralph Benjamin invented the trackball, then called a roller ball, in 1946 as part of a postwar radar plotting system called the Comprehensive Display System, choosing it as a more elegant alternative to a joystick for calculating the positions of target aircraft on an analog computer; the device was patented in 1947, though only a prototype using a metal ball rolling on rubber-coated wheels was built, and it remained a classified military secret while production versions of the display system used joysticks instead. Large trackballs remain common on computer-aided design workstations for precise work, smaller versions were once common on portable computers and on smartphones such as the BlackBerry before touchpads became standard, and some small clip-on thumballs attach to a keyboard with buttons matching those of a mouse.