Mouse Button - Scroll Wheel

Scroll Wheel

The scroll wheel, a notably different form of mouse-button, consists of a small wheel that the user can rotate to provide immediate one-dimensional input. Usually, this input translates into "scrolling" up or down within the active window or GUI-element. The wheel is often – but not always – engineered with a detent to turn in short steps, rather than continuously, to allow the operator to more easily intuit how far they are scrolling. The scroll wheel nearly always includes a third (center) button, activated by pushing the wheel down into the mouse.

The scroll wheel can provide convenience, especially when navigating a long document. In conjunction with the control key (Ctrl), the mouse wheel may often be used for zooming in and out; applications that support this feature include Adobe Reader, Microsoft Word, Internet Explorer, Opera, Mozilla Firefox and Mulberry, and in Mac OS X, holding the control key while scrolling zooms in on the entire screen. Some applications also allow the user to scroll left and right by pressing the shift key while using the mouse wheel.

Manufacturers may refer to scroll-wheels by different names for branding purposes; Genius, for example, usually brand their scroll-wheel-equipped products "Netscroll".

Mouse Systems invented the scroll wheel in the early 1990s, marketing it as the Mouse Systems ProAgio and Genius EasyScroll. However, mainstream adoption of the scroll wheel mouse did not occur until Microsoft released the Microsoft IntelliMouse in 1996. It became a commercial success in 1997 when their Microsoft Office application suite and their Internet Explorer browser started supporting its wheel-scrolling feature. Since then the scroll wheel has become a standard feature of many mouse models.

Some mouse models have two wheels, or wheels that can be moved sideways (such as the MX Revolution), separately assigned to horizontal and vertical scrolling. Designs exist which make use of a "rocker" button instead of a wheel – a pivoting button that a user can press at the top or bottom, simulating "up" and "down" respectively. A peculiar early example was a mouse by Saitek which had a joystick-style hatswitch on it.

A more recent form of mouse wheel is the tilt-wheel. Tilt wheels are essentially conventional mouse wheels that have been modified with a pair of sensors articulated to the tilting mechanism. These sensors are mapped, by default, to horizontal scrolling.

A third variety of built-in scrolling device, the scroll ball, essentially consists of a trackball embedded in the upper surface of the mouse. The user can scroll in all possible directions in very much the same way as with the actual mouse, and in some mice, can use it as a trackball. Mice featuring a scroll ball include Apple's Mighty Mouse and the IOGEAR 4D Web Cruiser Optical Scroll Ball Mouse. IBM's ergonomics laboratory designed a mouse with a pointing stick in it, envisioned to be used for scrolling, zooming or (with appropriate software) controlling a second pointer.

Some mice, like some models by Genius, have an optical sensor instead of a wheel. This sensor allows to scroll in both horizontal and vertical directions.