A scroll wheel is a wheel used for scrolling. The term usually refers to such wheels found on computer mice (where they can also be called a mouse wheel). It is often made of hard plastic with a rubbery surface, centred around an internal rotary encoder. It is usually located between the left and right mouse buttons and is positioned perpendicular to the mouse surface. Sometimes the wheel can be pressed left and right, which is actually just two additional macros buttons. Functionality The scroll wheel is placed horizontally between the mouse buttons and commonly uses vertical scrolling, wherein rolling the wheel from the bottom side to the top is known as scrolling "upward" or "forward", while the reverse, i.e. rolling the wheel from the top side to the bottom, is known as scrolling "downward" or "backward". In a graphical user interface, the "upward" motion moves contents of the window downward (and the scrollbar thumb, if present, upward), and vice versa. In other configurations (sometimes called "natural scrolling") the effect is inverted. On a mouse, the scroll-wheel can often also be used as a third mouse button by pressing down on it – a scroll button. Some mice can scroll horizontally as well as vertically, using a tilting scroll-wheel, or additional wheel on a perpendicular axis located elsewhere on the mouse. 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. Scroll wheels are prevalent on modern computer mice and have become an integral part of the hardware interface. However, non-wheeled mice are still available. Some user interfaces, like Cinnamon (desktop environment), allow using it to adjust brightness and volume by pointing at the respective taskbar icon while scrolling. History The scroll wheel on a mouse has been invented multiple times by different people unaware of the others' work. Other scrolling controls on a mouse, and the use of a wheel for scrolling both precede the combination of wheel and mouse. The earliest known example of the former is the Mighty Mouse prototype developed jointly by NTT, Japan and ETH Zürich, Switzerland (Kunio Ōno, Ken'ichi Fukaya and Jürg Nievergelt) in 1985. It had a thumb-operated combined analog button/toggle switch on the side for smooth scrolling. At the ACM SIGCHI conference in 1989, Gina Danielle Venolia