Computer trackball devices are commonly used to control the motion and position of a cursor on a video terminal screen. Trackballs are also used to input spatial translational and rotational coordinates into computer systems. A trackball consists of a ball which is supported within a housing and which is permitted to rotate in the housing. The ball protrudes through the top of housing so that the user can supply motive force directly to the ball at the point of protrusion. In operation, the cursor is moved to a desired location on the screen through movement of a roller ball by the user, and a specific function is then selected by pressing one or more keys on the control device. Rotation of the ball by the user is transferred into two orthogonal directions such as X and Y coordinate directions to move the pointer on the computer screen in the X and Y directions.
