Fitts's Law

A predictive model of human movement that describes the time required to rapidly move to a target area as a function of the distance to the target and the size of the target. Formulated by Paul Fitts in 1954, the law states that movement time increases logarithmically as the distance increases or target size decreases. In accessibility research, Fitts's Law is widely used to evaluate the performance of input devices and pointing methods — including alternative inputs like head tracking, eye gaze, and switch scanning — by measuring throughput (bits per second), which allows standardized comparison across different interaction techniques and user populations.