Off table and without limitation of operational space 4D page scrolling function can be controlled simply by your thumb Features 3-button design with trackball USB 2.0 interface, plug and play, no software required. Special design, can avoid the harm on your wrist and muscle, greatly reduces discomfort for Arthritis and CTS suffers Easy to use - left or right hand, or cradled between both Mini size, light weight, easy to carry Ideal for both laptops and desktops Place end of index or middle finger on trigger button & thumb on roller ball Compatible with Windows 95 version B / 98 / ME / 2000 / XP / NT