Improving scrolling devices with document length dependent gain.

We describe a method for applying gain to events reported by scrolling input devices such as scroll wheels. By treating document length as an input to our gain functions, the method allows rapid document traversal regardless of document length; it also allows slow and precise scroll control at shorter distances. An initial experiment characterises four diverse scrolling input devices -- a standard 'notched' scroll wheel, a high performance 'inertial' wheel, an isometric scrolling joystick, and a trackpad -- and the results are used to calibrate several gain function parameters. A second experiment validates the method, showing that it allows faster scrolling in long and short documents than current scrolling-device gain methods, and that subjective preferences favour it.