Logitech Cordless Trackman Optical Trackball mouseAn input device that looks like an upside-down mouse. The onscreen pointer is moved by the trackball with a thumb or finger. A trackball requires less arm and wrist motion that a regular mouse takes and therefore is often less stressful for the user to use, helping to prevent RSI. In the picture to the right, is a Logitech Cordless Trackball mouse and an example of what a trackball mouse may look like.

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Also see: Mouse, Mouse terms, Pointing device