<P> A scroll wheel (or mouse wheel) is a hard plastic or rubbery disc (the "wheel") on a computer mouse that is perpendicular to the mouse surface . It is normally located between the left and right mouse buttons . </P> <P> It is used, as the name suggests, for scrolling . It can often also be used as a third mouse button by pressing on it . The wheel is often--but not always--engineered with detents to turn in discrete steps, rather than continuously as an analog axis, to allow the operator to more easily intuit how far they are scrolling . </P> <P> Some modern mice can scroll horizontally as well as vertically, using a tilting scroll - wheel (introduced by Microsoft), scroll ball (found, for example, on Apple's Mighty Mouse), pointing stick, touchpad (as on Apple's Magic Mouse), optical sensor, or a second scroll wheel . Logitech mice with' Free Spinning' scroll wheels use a 14 gram scroll wheel with high rotational inertia like a flywheel that can be used to quickly scroll through long pages and lists . A peculiar early example was a mouse by Saitek which had a joystick - style hatswitch on it . </P>

Some mice have a wheel in the middle. generally what is this wheel for