A trackball mouse is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes—like an upside-down ball mouse with an exposed protruding ball. Users roll the ball to position the on-screen pointer, using their thumb, fingers, or the palm of the hand, while using the fingertips to press the buttons. With most trackballs, operators have to lift their finger, thumb or hand and reposition in on the ball to continue rolling, whereas a mouse would have to be lifted itself and re-positioned. Some trackballs have notably low friction, as well as being made of a dense material such as phenolic resin, so they can be spun to make them coast. The trackball's buttons may be in similar positions to those of a mouse, or configured to suit the user. Large trackballs are common on CAD workstations for easy precision. Before the advent of the touchpad, small trackballs were common on portable computers (such as the BlackBerry Tour) where there may be no desk space on which to run a mouse. Some small "thumballs" are designed to clip onto the side of the keyboard and have integral buttons with the same function as mouse buttons. History The trackball was invented as part of a post-World War II-era radar plotting system named Comprehensive Display System (CDS) by Ralph Benjamin when working for the British Royal Navy Scientific Service. Benjamin's project used analog computers to calculate the future position of target aircraft based on several initial input points provided by a user with a joystick. Benjamin felt that a more elegant input device was needed and invented a ball tracker system called the roller ball for this purpose in 1946. The device was patented in 1947, but only a prototype using a metal ball rolling on two rubber-coated wheels was ever built and the device was kept as a military secret. Production versions of the CDS used joysticks. The CDS system had also been viewed by a number of engineers from Ferranti Canada, who returned to Canada and began development of the Royal Canadian Navy's DATAR system in 1952. Principal designers Tom Cranston, Fred Longstaff and Kenyon Taylor chose the trackball as the primary input, using a standard five-pin bowling ball as the roller. DATAR was similar in concept to Benjamin's display, but used a digital computer to calculate tracks,