Fitts’ Law

Fitts' Law: The time to acquire a target is a function of the distance to and size of the target.

[Fitts 54], [Fitts/Peterson 64]

Index of difficulty = log₂(2d/w)
where d is the distance to target and w the width of the target

Time to point = c₁ + c₂ * (Index of difficulty) where c₁ and c₂ are device dependant constants.

[Smith et al. 82]

[The mouse] is a “Fitts’s Law” device. That is, after some practice you can point with a mouse as quickly and easily as you can with the tip of your finger. The limitations on pointing speed are those inherent in the human nervous system.

[Card et al. 83]

time for reaching the target for a single-level pull-down = 1.08 + 0.096 log₂(d/w +0.5) sec
where w is the height of the menu item

Doug Engelbart and Bill English concider the mouse as a interim device. Bill English tried to develop a device that is faster than the mouse, but the mathmatical equation of the mouse is pretty much the same than a plain hand pointing action. Therefor the speed limiting factor is not the mouse device but the eye-hand coordintae system itself.

“Furthermore, the model provided guidance for interface designers: make distant buttons large, for example. These studies were heavily used in the debate within Xerox that lead to the decision to depart from tradition by including a mouse with the new Star product.”

[Walker/Smelcer 90]

The border of the screen is infinite.

Mouse movements constraints to be added to border of popup menus, to top of windows if it containes a menu bar like Windows™ can speed up menu access.

[Sears/Shneiderman 91]

Fitts’ Law applied for high-precision touchscreens. Added elements to the definition to reflect fine-tuning motions of fingers [Shneiderman 98, p. 325]

[Tognazzini 92, p. 201]

[MacKenzie 92]

describes lucidly what Fitts’ Law is, how it has been applied, and what the many refinements are, i.e. two dimensional pointing

[Baecker et al. 95, p. 470]

Fitts’ Law first used to study HCI in [Card et al. 78] (Card, Stuard K. / English, William <Bill> / Burr, B.), also [English et al. 67] (English, William <Bill> / Engelbart, Doug / Berman, M.)

[Accot/Zhai, 97]

For a two-dimensional target, you can usually obtain a reasonable approximation of the time needed to move the cursor to the target, using the samaller of the horizontal and vertical dimensions of the target for the value w. [Raskin 2000, p.94]