Trackball
It is an input device which is used to enter motion data into computers or other electronic devices. It is invented by tom Cranston and Fred longstaff in 1952. It consists of a ball held by a socket containing sensors to detect a rotation of the ball about two axes. It is like an upside-down mouse with a ball that sticks out. The user rolls the ball with the thumb, fingers or the palm of the hand to move a cursor.
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