Mouse Tracking Speed
From Mac Guides
- This article or section is based on a forum post written by portent.
Computer mice must convert the motion of the mouse across a surface to the motion of the on-screen mouse pointer. The translation between the physical and on-screen motions is determined by an algorithm (a mathematical, two-dimensional function) that adjusts the rate to allow for both rapid and precise mouse targeting. When the mouse is moved a given distance slowly, the pointer will move a shorter distance than if the mouse is moved that same distance quickly.
Adjusting tracking speed
In System Preferences, in the Mouse or Keyboard and Mouse pane, there is an option to adjust the tracking speed. The "slow" settings bias movement for greater precision; the "fast" settings bias the movement for greater travel.
Mac OS X uses a different algorithm than does Microsoft Windows and other operating systems. For users accustomed to Windows, Apple's default mouse tracking may seem unusual. Some call it "slow" or "sluggish." 
A number of software add-ons replace the default tracking algorithm. One popular one is USB Overdrive, which also offers a variety of customizations.
Testing the default tracking algorithm
Many reports on the web complain that the mouse tracking speed (or acceleration) is not sufficient under Mac OS X, especially with a large (or high-resolution) display. This guide attempts to investigate this claim in a verifiable and conclusive manner.
- Mouse used: Apple Wireless (Bluetooth) Model A1015
- Operating System: Mac OS X 10.4.7 (Tiger)
- Mouse tracking speed: 6th notch; three notches shy of the "fast" setting
- Mousing surface: Tucano Bunny (MPDEL-179) textured-plastic surface, 19.7cm wide by 22.9 cm high; ("portrait" orientation as depicted in link)
- Desktop size: 2048 x 768 pixels; (dual-display 1024x768, side-by-side virtual orientation)
- Measuring device: Wescott wooden meterstick
No haxies or alternative drivers were installed on the test system.
Prior to testing, the bottom of the mouse was cleaned with a dry Kleenex facial tissue. The mousepad was likewise wiped with facial tissues.
The mouse itself was positioned along the extreme left edge of the mousepad; a straightedge was used to align the mouse and mousepad edge. The mouse pointer was positioned at the extreme left of the display (The trackpad was used to move the pointer when necessary, so as not to distrub the position of the mouse.) An operator moved the mouse in a rapid motion until he determined that the mouse pointer had reached the extreme right of the display area. At this point he released the mouse.
A measurement was taken of the horizontal distance between the left edge of the mousepad (the starting point) and the resting position of the mouse (the ending point) and the experiment was repeated an additional four times. Anomalous or unsuccessful movements were rejected.
- Metric: 4.3cm, 5.4cm, 4.2cm, 5.0cm, 4.6cm
- Imperial: 1.7", 2.1", 1.7", 2.0", 1.8"
Calculation of rate
The average (arithmetic mean) distance required was 4.7cm. Using the following formula
r = p / d
where r is the rate in pixels/cm, p is the number of horizontal pixels, and d is the horizontal distance travelled, the average tracking speed observed was 435.7 pix/cm.
Among the highest-resolution displays on the market is the 30-inch Apple Cinema HD Display. It has an horizontal resolution of 2560 pixels. If one assumes that the widest practical display configuration is two of these displays, configured side-by-side in a virtual desktop, the maximum horizontal distance that could it concievably be necessary to traverse is 5120 pixels.
The mousepad used in this experiment has a width of 19.7cm. The mouse used has a width of 6.1cm. This results in 13.6cm of available horizontal space for motion. At the average rate of travel calculated above, this is sufficent to allow an operator to traverse 5926 pixels --significantly larger than our theoretical maximum--without exceeding the boundaries of a commonly available mousepad.
The testing above applies only to the mouse and driver (the Mac OS X default) examined. Presumably, other Apple mice, including the USB single-button optical and the Mighty Mouse, as well as other mouse devices which use similar tracking mechanisms and the Mac OS X driver, would perform similarly. Mice which use substantially difficult tracking mechanisms will perform differently.
The performance is also dependent on the skill and experience of the operator. Many of the complaints linked in the introduction are from people who have only recently come to use Macintosh computers and Mac OS X.
The mouse acceleration and tracking speed under Mac OS X are sufficient to allow an experienced operator to traverse an arbitrarily large desktop without exceeding the bounds of an ordinary mousepad. Any difficulties experienced by users are likely due to a lack of familiarity working with the mouse or operating system in use.