Editing Scroll wheel

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[[File:Scroll wheel.jpg|thumb|250px|Tilt-wheel scroll wheel on a Logitech mouse]]

A '''scroll wheel''' is a vertically-oriented, typically rubber-coated wheel that sits between the left and right buttons of a [[mouse]]. Similar functionality exists on some [[trackball]]s as well.

Scroll wheels are typically about 1 inch in diameter and 8 mm thick.

==Functionality==

===Scrolling===
Rotating the wheel sends vertical scroll commands in many graphical desktop systems. In many systems, the panel or control under the cursor is scrolled; in [[Microsoft Windows]], however, it's far more common for the scroll events to be sent to whichever control has the focus. This behaviour can be modified through many programs.

Most wheels have tactile detents (notches), each corresponding to a scrolling step. There are typically 24 detents per revolution, but some wheels have only 18.
When a electromechanical [[rotary encoder]] is used, the detents tend to be a property of it. When an optoelectric encoder is used instead, the detents are created by a separate spring.

In Microsoft Windows, each step is a fixed amount of three lines of text.
Faster rotation of the wheel in some systems, including in Apple's [[macOS]], increases the scroll distance per step to provide accelerated scrolling.
Scrolling acceleration is also provided as a feature in the Microsoft IntelliPoint driver software supplied with the IntelliMouse.

===Smooth scrolling===
In [[Microsoft Windows|Windows ''Vista'']], Microsoft introduced a protocol on top of [[USB|USB HID]] for smoother scrolling with higher resolution than per detent.

When a mouse powers up it should not do smooth scrolling by default but when Windows boots it would tell the mouse to increase its resolution.<ref>Microsoft - [http://www.microsoft.com/whdc/device/input/wheel.mspxEnhanced Wheel Support in Windows]. Dated 2010-11-10. Retrieved 2016-04-06.</ref>

However, some of [[Microsoft]]'s own mice suffer from a bug that it does not reset its internal resolution when the host reboots. This has the effect that when users dual-boots from Windows into an operating system that does not support the protocol, 
scrolling is much too fast. Workarounds includes power-cycling the mouse (re-plugging) and to run a specific utility which sends the mouse the appropriate message.<ref>Ubuntu Answers - [https://answers.launchpad.net/ubuntu/+question/9200 Change scroll wheel speed].Retrieved 2016-10-30.</ref>

===Mouse button three===
Most scroll wheels work as mouse button three when pressed straight down.
The button is often heavier than other buttons.

PC mice before scroll wheels traditionally followed two competing standards: Logitech's and Microsoft's. Logitech favoured three-button mice, and Microsoft favoured two. First with [[Microsoft]]'s first scroll wheel-equipped [[Microsoft IntelliMouse|IntelliMouse]], did they make the transition of three-button mice, but putting it under the wheel.

This non-obvious functionality, together with traditionally limited adoption by Windows and software applications, has lead to a general lack of awareness of this additional button. The number of websites that fail to accept middle-click to open links in a new tab suggests how many web designers alone remain oblivious to this facility.

==Variations==
[[File:Free tilt wheel.jpg|250px|thumb|right|Tilting scroll wheel. The button behind it toggles between detents/free motion]]
===Dual axis scrolling===
====Dual scroll wheels====
A few mice featured dual scroll wheels, one per axis. These could be arranged parallel or perpendicular to each other. This design is quite rare, and dual-axis scrolling now is typically achieved using a tilt wheel.

====Tilt wheel====
A tilt wheel is a scroll wheel than can be leaned sideways to achieve sideways scrolling. This tends to come at the cost of reliable middle button action.

===Free motion wheel===
The mouse wheel typically moves in precise steps defined by mechanical detents. These wheel notches allow for precise scrolling.

Some wheels, such as that of the Microsoft Comfort Mouse 4500, rotate freely without detents slowing it down. Scrolling through a document slowly requires particular practice.

Some mice can switch between having detents and free motion.
On some mice there is a latching button next to the wheel (or inconveniently ''under'' the mouse) which switches between the two modes.
On some other mice the button is in the scroll wheel instead of a third mouse button.

A ''speed-adaptive scroll wheel'' deactivates detents automatically when the wheel is spun fast enough.

==Alternatives==
===Scroll ball===
[[File:AppleNotSoMightyMouse.jpg|250px|thumb|right|[[Apple A1152]] mouse (2005) with a miniature scrolling ball. It was the first Apple mouse that supported scrolling]]
Omega's ''3D Magic Optical Scrolling Mouse''<ref>Microsoft Research, Buxton Collection—[https://www.microsoft.com/buxtoncollection/detail.aspx?id=144 4D Magic Optical Scrolling Mouse]. Retrieved 2019-02-09</ref> and [[Apple A1152]] have each instead of a wheel, a small [[trackball]] that allows two-dimensional scrolling.

===Scroll toggle===
Some pointing devices have a special button that while held turns the device into a scrolling device.

In xorg, an implementation of the [[X Window System]] (the de-factor standard under Linux and most Unix systems), any button can be turned into such a toggle.
Open (or create) the file /etc/X11/xorg.conf.d/10-evdev.conf and add the following section:

<pre>
Section "InputClass"
   Identifier  "Mouse0"
   Driver "evdev"
   MatchIsPointer "on"
   MatchDevicePath "/dev/input/event*"

   Option "EmulateWheel" "true"
   Option "EmulateWheelButton" "9"

   Option "ZAxisMapping" "4 5"
   Option "XAxisMapping" "6 7"
EndSection
</pre>

The example above makes the button #9 (usually the forward button) into a scrolling-toggle button.

===Scrolling stick===
[[File:IBM MO098O.jpg|250px|thumb|right|IBM MO098O ScrollPoint mouse]]
[[IBM]]'s ''TrackPoint Mouse'' series had an analogue [[TrackPoint]] for scrolling in two dimensions.
Later ''Scrollpoint'' models (also [[Lenovo]]) had a larger analogue [[joystick]] more shaped like a mouse button.

Researchers at IBM have done user testing that showed the scrolling stick to be both faster and more preferred by their test users over the scroll wheel<ref name="zhai97">Shumin Zhai, Barton A. Smith, Ted Selker ''Dual Stream Input for Pointing and Scrolling''. Proceedings of the ACM CHI 97 Human Factors in Computing Systems Conference</ref>.
It does however require a driver or tweaked settings to reduce sensitivity, or the stick will scroll too fast for normal use.

===Rocker switch===
''Genius NetMouse'' series have a flat rocker-button in-between left and right mouse buttons that can be pressed forward or back.<ref name="tcodnetmouse">The Collection of Calculating Devices—[http://www.tcocd.de/Pictures/Peripheral/Genius/netmouse.shtml Genius NetMouse]. Retrieved 2021-03-14</ref>.

''Genius NewScroll'' and ''Mitsumi Scroll Mouse'' have a smaller knob that can be rocked forwards and backwards instead of a flat button, but work the same way.<ref name="ixbdnewcroll">iXBT Labs—[http://ixbtlabs.com/articles/mousestesting13models/index.html Mouses: testing 13 models]. Retrieved 2021-03-15</ref>
Unlike a TrackPoint/ScrollPoint these are digital and scroll only vertically.

===Scroll ring===
Some of the [[:Category:Kensington trackballs|trackballs from Kensington]] have a rotating ring around the [[trackball]] for scrolling. It was introduced with the [[Kensington TurboRing]] (2000) and then later in the [[Kensington Expert Mouse]] in 2003.<ref name="KisselEvolutionOfScrolling">Interesting Thing of the Day—[https://itotd.com/articles/330/the-evolution-of-scrolling-classic/ The Evolution of Scrolling]] by Joe Kissel. Dated 2004-10-07. Retrieved 2018-12-04</ref>

===Touch surface===
There are now many mice that use a touch-sensitive surface instead of scrollwheel.

Some use a wide touch surface for horizontal swipes and even taps for such actions as "Back" and "Forward".
In such designs the touch-surface could interfere with the action of the [[mouse button]]s.
On [[Apple]]'s ''Magic Mouse'' the whole touch surface is titled to click, with left and right [[mouse button]]s distinguished only by which area of the surface that has a finger. This does not allow a finger to be resting on the left button while the right button is clicked.

==History==
The scroll wheel on a mouse has been invented multiple times by different people unaware of each-other's work.  Other scrolling controls on a mouse, and the use of a [[spinner]] for scrolling both precede the combination of ''wheel-on-mouse''.
The earliest known wheel shown to the public was a research project from [[Apple]] at a conference in 1989<ref name="buxtontimeline"/> followed by [[Three degree of freedom graphic object controller|a patent]], applied for in 1992.

The first mouse with scroll wheel available on the market was the ''[[Mouse Systems]] ProAgio Scroll Mouse'' from  in 1995. It was also sold as the ''Genius EasyScroll''.
<ref name="oldmouseProAgio">Oldmouse.com—[https://www.oldmouse.com/mouse/mousesystems/scroll.shtml Mouse Systems ProAgio Scroll Mouse]. Retrieved 2018-12-04</ref>

[[Microsoft]] popularised the scroll wheel with the [[Microsoft IntelliMouse|IntelliMouse]] in 1996.

IBM's [[#Scrolling stick|TrackPoint Mouse]] was the first commercial mouse with two-dimensional scrolling.<ref name="buxtontimeline">BillBuxton.com—[https://www.billbuxton.com/inputTimeline.html Some Milestones in Computer Input Devices: An Informal Timeline]. Revision dated 2018-11-23, retrieved 2018-12-04</ref>

==References==
<references/>

[[Category:Pointing device terms]]