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Citation (published version)Greg Blonder. "Computer trackball." U.S. Patent 5,620,371-A.
A computer trackball comprises a transparent outer sphere inside of which is disposed a second inner sphere. The outer diameter of the inner sphere is a little bit smaller than the inner diameter of the outer sphere. Disposed on the outer surface of the inner sphere, at one "end" thereof is a logo or other graphical image. The inner sphere tends to maintain itself in a predetermined orientation--e.g., with the graphical image pointing directly "up" relative to the keyboard or other housing fin which the trackball is held--notwithstanding rotation of the outer sphere by a user in the course of operating the trackball.