“The key statement of Fitts’s Law is that the time required to move a pointing device to a target is a function of the distance to the target and its size. In layman’s terms: the closer and larger a target, the faster it is to click on that target. This is easy to understand, not too difficult to implement and it doesn’t seem to make much sense to contradict such a simple and obvious statement.”
When You Shouldn’t Use Fitts’s Law To Measure User Experience
Fitts’ law is a principle for UI design; not an evaluation method for UX.