The difficulty of “acquiring a target” (such as using a mouse to click on an icon on a computer screen) depends on the ratio between the distance D to the target and width W of the target. According to Fitts’ law, the index I of difficulty is modeled by

This law is used for designing products that involve human–computer interactions.

(a) If W is held constant, what is the rate of change of I with respect to D? Does this rate increase or decrease with increasing values of D?

(b) If D is held constant, what is the rate of change of I with respect to W? What does the negative sign in your answer indicate? Does this rate increase or decrease with increasing values of W?

(c) Do your answers to parts (a) and (b) agree with your intuition?

Transcribed Image Text:

2D I= log 2 W