Unlike the mechanical-trackball "mice of yore" that skip, stick, and need to be cleaned, the Microsoft TrackBall Optical introduces an entirely new trackball featuring optical sensor technology. Reading through dirt, dust, and fingerprints, the optical sensor tracks the movement of the ball 1,500 times per second, giving you smooth, precise control. The Trackball Optical comes with two additional buttons located on the side of the device--for a total of five buttons--to quickly move forward and back in your browser, or you can program them. It also features a wheel for efficient scrolling and zooming and is ergonomically designed to support the natural position of your hand as you use your thumb to control the trackball.
A trackball mouse that uses revolutionary optical technology for high-precision mousing Other features include - programmable forward & back buttons Scroll wheel Comfortably designed shape that supports your right hand in a natural position Supports Windows and Macintosh systems with USB connections