Fitts' Law

A predictive model of human movement in human-computer interaction that states the time required to move to a target area is a function of the distance to the target and the size of the target. Specifically, larger and closer targets are faster to acquire than smaller and more distant ones. Originally developed for physical pointing tasks, Fitts' Law has been widely applied to UI design for mouse cursors, touch targets, and other input methods. Research with screen reader users on touchscreens has shown that while the general principle holds for non-visual target acquisition (larger targets on smaller search spaces are faster), the relationship is more complex because the screen-to-target ratio and exploration strategy also significantly affect performance in ways not captured by the traditional model.