The LEFT Hand - Evoluent Std. Vertical Mouse 4 - New and Improved has a patented new shape that supports your hand in a relaxed handshake position and eliminates arm twisting. Once you experience the superior comfort, you will never go back to ordinary mice. Features Include: * 1200 dpi true optical resolution sensor reduces hand movements compared to other mice which generally have 800 dpi. * 5 buttons -- 4 are programmable with 59 selectable functions each with Windows driver, plus special features such as: Vertical scroll - press a button and drag the mouse to scroll with greater precision and control than the scroll wheel. Auto click - automatically perform a double click by pausing the pointer. Click lock - press and hold a button momentarily to simulate continued pressing without holding down the button. * Compatible with PC, Mac, UNIX and Linux Versions.