Editing Fitts's law (section)

=== Extensions to two or more dimensions ===
In its original form, Fitts's law is meant to apply only to one-dimensional tasks. However, the original experiments required subjects to move a stylus (in three dimensions) between two metal plates on a table, termed the reciprocal tapping task.<ref name=Fitts1954/> The target width perpendicular to the direction of movement was very wide to avoid it having a significant influence on performance. A major application for Fitts's law is 2D virtual pointing tasks on computer screens, in which targets have bounded sizes in both dimensions.

[[File:Reciprocal Tapping Task.jpg|thumb|Reciprocal Tapping Task in a 2D context]]

Fitts's law has been extended to two-dimensional tasks in two different ways. For navigating e.g. hierarchical pull-down menus, the user must generate a trajectory with the pointing device that is constrained by the menu geometry; for this application the [[Accot-Zhai steering law]] was derived.

For simply pointing to targets in a two-dimensional space, the model generally holds as-is but requires adjustments to capture target geometry and quantify targeting errors in a logically consistent way.<ref name=Wobbrock2011>{{cite conference|last1=Wobbrock |first1=J. |last2=Shinohara |first2=K |title=Proceedings of the SIGCHI Conference on Human Factors in Computing Systems |chapter=The effects of task dimensionality, endpoint deviation, throughput calculation, and experiment design on pointing measures and models |date=2011 |pages=1639–1648 |location=Vancouver, British Columbia |doi=10.1145/1978942.1979181 |isbn=9781450302289 |citeseerx=10.1.1.409.2785 |s2cid=18568166 }}</ref><ref name=MacKenzie1992-2D>{{cite book |last1=MacKenzie |first1=I. Scott |first2=William A. S. |last2=Buxton |title=Proceedings of the SIGCHI conference on Human factors in computing systems - CHI '92 |chapter=Extending Fitts' law to two-dimensional tasks |date=1992 |pages=219–226 |url=http://www.yorku.ca/mack/CHI92.html |doi=10.1145/142750.142794 |isbn=978-0897915137 |s2cid=358907 }}</ref>
Multiple Methods have been used to determine the target size&nbsp;:<ref name="Zhao2002">{{cite journal |title=Fitt's Law: Modeling Movement Time in HCI |journal=Theories in Computer Human Interaction |year=2002 |last=Zhao |first=H. |s2cid=17219815 }}</ref>

* status Quo: horizontal width of the target
* sum model: ''W'' equals height + width
* area model: ''W'' equals height * width
* smaller of model: ''W'' smaller value of height and width
* W-model: ''W'' is the effective width in the direction of the movement

While the ''W''-model is sometimes considered the state-of-the-art measurement, the truly correct representation for non-circular targets is substantially more complex, as it requires computing the angle-specific convolution between the trajectory of the pointing device and the target <ref name=Grossman2005>{{cite journal |title=A probabilistic approach to modeling two-dimensional pointing. |journal=ACM Transactions on Computer-Human Interaction |last1=Grossman |first1=Tovi |last2=Balakrishnan |first2=Ravin |date=September 2005 |volume=12 |issue=3 |pages=435–459 |url=https://doi.org/10.1145/1096737.1096741 |doi=10.1145/1096737.1096741|s2cid=8809382 |citeseerx=10.1.1.61.5707 }}</ref>