Logitech TrackMan Marble FX features a revolutionary four-button design that offers a fresh choice for comfort in a finger-operated trackball. It combines a large ball with the most advanced pointing technology available today, Logitech is patented Marble sensing technology. You get smooth motion, enhanced reliability, and superior precision in a trackball that is so dirt resistant it doesn't require regular cleaning.??Place your hand on TrackMan Marble FX and you'll feel the Marble difference. This is the only finger-operated trackball that lets you move the ball with just your finger, or use your finger and thumb for fine detail work. Logitech patented Marble sensing technology replaces all the mechanical moving parts that record motion with an optical tracking system. A laser-like beam illuminates dots printed on the ball, while a sensor tracks the motion. This gives you precision, reduces wear, and ensures smooth tracking even if the ball gets dirty or scratched. Only TrackMan ...