The thumb-operated Logitech® TrackMan® Marble®+ trackball combines outstanding comfort with the superior performance of patented Marble sensing technology. An innovative scroll wheel that's also a third mouse button provides fast scrolling in any Windows® 95 Windows® 98 or Windows NT® 4.0 application, and the Internet. Also scroll and zoom in Microsoft® Office® 97. Optical Marble technology provides unmatched reliability and precision, and eliminates the need for regular trackball maintenance. Marble technology and a sleek trackball design offer convenient thumb control and fast, precise cursor movement. Customize performance by assigning one-click commands, including draglock and double click, to the buttons with MouseWare® software.Three-year warranty. Scrolling requires Windows® 95 or Windows NT® 4.0. Windows® 3.1 compatible.