hardware A pointing device consisting of a ball housed in

a socket containing sensors to detect rotation of the ball

about two axes - like an upside-down mouse. The user rolls

the ball with his thumb or the palm of his hand to move a

cursor. Tracker balls are common on CAD workstations for

ease of use and on modern portable computers, where there

may be no desk space on which to use a mouse. Some clip

onto the side of the keyboard and have integral buttons which

have the same function as mouse buttons.