The Fitt's Law was born with Paul Fitts, US Air Force researcher, who did an experiment in which he analyzed how much time it took a person to move source to destination, considering distance and width.
The formula is,
The formula is,
In the equation above :
- Time (T) is the amount of time required to complete the movement.
- a and b are empirically determined regression coefficients, which is basically a fancy way of stating they are values gained from direct observation that build a slope.
- Distance (D) is a measurement from the starting point to the end point (target object).
- Width (W) is the width of the target object.
Zero distance :
- If our starting point is that we want to do interfaces where is really easy to click on something, it means that movement should take almost no time, i.e. T=0; if T=0, then we need zero distance and infinite width.
- A perfect example of zero distance is the context menu that pops up several operating systems when we right-click on something.
- It is incredibly easy to use, because we have no distance to move to the first action, and no distances between other actions.
Movement and Distances :
Apart from size of the target object, another primary factor in Fitts’ law is the distance from source to target object.
