Trackball

A trackball 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 mouse with an exposed protruding ball. The user rolls the ball with the thumb, fingers, or the palm of the hand to move a pointer. Compared with a mouse, a trackball has no limits on effective travel; at times, a mouse can reach an edge of its working area while the operator still wishes to move the screen pointer farther. With a trackball, the operator just continues rolling (however, it could be argued that a mouse user could simply increase sensitivity and/or increase mousepad size to avoid this problem) Some trackballs, such as Logitech's optical-pickoff types, have notably low friction, as well as being dense (glass), so they can be spun to make them coast.The trackball's buttons may be situated to that of a mouse or to a unique style that suits the user.