Now two thumb buttons A new bottom thumb button provides greatly extended functionality when used with the included driver. Extended lip prevents rubbing An extra wide lip along the bottom edge prevents the last finger from rubbing the desk. Avoids forearm twisting for comfort and good health* The patented shape supports your hand in an upright neutral posture that generally avoids forearm twisting. Many users, including medical doctors, ergonomists and physical therapists, said the Evoluent Vertical Mouse provides superior comfort and even relieved their wrist pain.Adjustable optical sensor Pointer speed controls on the side allow convenient adjustment without even releasing your grip from the mouse. Pointer speed indicators Top mounted LEDs show through the chrome thumb rest to indicate selected pointer speed including extra low (XL), low (LO), MD (medium), to high (HI Powerful and intuitive driver Evoluent Mouse Manager for Mac provides extensive but easy to use functionality for 6 buttons through a simple Bluetooth connectivity that connects to Mac systems via Bluetooth andd intuitive interface.