Fitts' law - Computer Definition
"The time required to reach a target is based on the distance from the starting point and the size of the target." Coined by Paul Fitts in the 1950s, the law is applied to the location and size of menus and buttons in software. For example, a large button is faster to reach than a small one, and the edges of the screen provide natural stops. Many users prefer the Mac's user interface, because all menus display at the top of the screen. Others prefer Windows, because many commonly used buttons can be made much larger. See laws.