Paul Fitts was a psychology professor at Michigan and Ohio State, who had served in the Air Force and used an ergonomic model to improve safety in military aircraft.
His most important contribution to human-computer interaction is the eponymous Fitts’ Law, which gives a mathematical basis for determining how easy or difficult it is to interact with a target on an input device.
Fitts’ measurement for the effectiveness of a target can be calculated using , where is the distance to the target, is the width of the target, is the average movement time to the target, and is “throughput”. The best strategies for selection targets maximize throughput.
A regression model based on this equation was used at Xerox in the 1970s to evaluate different pointing devices, leading to the mouse becoming the standard for pointing device for GUIs for 30 years (the trackpad and touch screen are now arguably more popular). It gave the greatest throughput of anything evaluated.
The lasting impact of having a mathematical basis for understanding an interface’s effectiveness leads to being able to prove certain HCI design principles that seem intuitive, e.g.:
- Frequently used targets should be larger or closer to the pointing origin, making them easier to access.
- Dangerous targets should be smaller and moved farther away from the pointing origin, to give extra time for the user to process whether it is the correct action.
- With motion based pointing devices (mouse, joystick, etc.), the easiest places to access in an interface are the corners, followed by the edges.