exercises

2. the computer

EXERCISE 2.6

Describe Fitts' Law (see chapter 1). How does Fitts' Law change for different physical selection devices, such as a 3-button mouse, a touchpad, or a pen/stylus? (You'll need to do some research for this.)

answer available for tutors only

There should be an attempt to write down Fitts' Law in one of its many forms. The form students may be most familiar with is:

Movement time = a + b log2(distance/size + 1)

The relationship between time and distance and size of a target should be expressed. Students should know what the time stands for (time for selecting a target) and that distance and size are descriptions of the target.

They should be able to adequately explain that the constants in the formula are there to calibrate for different selection techniques (3-button mouse, trackpad, pen, etc.). They may simply mention that the law changes for different selection mechanisms, or, more explicitly, mention a and b parameters.

NB There are more forms of Fitts' Law than the one above, but the important parts are the constants and the time/distance/size relationships.

Other exercises in this chapter

ex.2.1 (open), ex.2.2 (tut), ex.2.3 (open), ex.2.4 (tut), ex.2.5 (tut), ex.2.6 (tut), ex.2.7 (ans), ex.2.8 (ans), ex.2.9 (open)

all exercises for this chapter