Kensington Expert Trackball Mouse

The Expert Mouse Trackball by Kensington features Diamond Eye Optical tracking for accuracy, a Scroll Ring for precise fingertip scrolling, a large ball for maximum precision and control and a
detachable wrist rest. Computer requirements:
a PC running Windows 98 or later with an available USB or PS2 port, a Mac running OS X or later with an available USB Port.
The computer must have an Internet connection or CD ROM drive to install the software.