The Perfit Mouse Optical, model PMO, and Classic Plus, model PMO5, is a mouse designed for use by people with upper extremity or fine motor disabilities. Intended to allow maximum muscle and tendon variation during point and click operations, the both models feature sculpted elevated buttons designed to enable the hand to remain open with the fingers extended in a ready position for quick button activation and to reduce excessive load on the fingertips. The buttons can be programmed to perform selected functions. There is a thumb support with a two- position side rocker switch that uses very light touch internal switches and are designed not to require pinch force to activate. The switches "click" with a very slight forward or backward motion of the thumb. The switch rocker is rubber coated and textured to provide maximum grip, with little effort. The Perfit Mouse Optical features a scroll wheel integrated into the thumb support. There is also an elevated wrist support integrated in the mouse’s design. The mouse uses an 800 dots per inch (dpi) optical sensor to track its movement by the user. This mouse is fitted for both right and left hands. COMPATIBILITY: For use on IBM PC and Macintosh computers (USB and PS2). The Perfit Mouse in compatible with Windows, Macintosh, Sun and Linux operating systems. SYSTEM REQUIREMENTS: Some operating systems may require installation of driver software. SIZES: Extra large (right hand only), large, medium, or small. COLOR: White. WARRANTY: 30-day money back guarantee.