This mouse delivers comfortable fit with optical performance. Optical tracking means smooth control, no need for regular cleaning. And comfortable design ensures the long hours of use. Logitech Marble Mouse now provides two ways to scroll without a scroll wheel. Two additional buttons let you scroll up or down a page or click the large buttons together and use the ball for auto scrolling. Marble Mouse fits right and left hands like a mouse and works with the convenience of a trackball. Patented Optical technology provides superior precision and smooth motion, and eliminates the need for regular cleaning. Enjoy the fit you love in a mouse, yet just move the trackball instead of moving the whole mouse around. It saves desk space, reduces hand and wrist movement.