Mouse Systems' PC Trackball II redefines the input device by providing a compact, responsive, comfortable trackball. The PC Trackball II provides fingertip control of your system by combining 350 cpi resolution, comfortable ergonomics and 100% Microsoft, Mouse Systems and PS/2 compatibility.??Coupled with Mouse Systems' acclaimed drivers, the PC Trackball II can achieve resolutions of up to 30, 000 counts per inch (cpi). The Trackball II also provides a variety of acceleration curves and button reassignments (perfect for left-handed users).