Physical Principles

Question 1

What are the three types of pointer movements?

Answer 1

Tracked movement
Dragged movement
Disengaged movement

Question 2

Describe tracked movement

Answer 2

A mouse device is tracked by the system and represented by the cursor position

Question 3

Describe dragged movement

Answer 3

A mouse also can be used to manipulate screen elements using drag and drop operations

Question 4

Disengaged movement

Answer 4

Some pointing devices can be moved without being tracked by the system, such as light pens or fingers on a touchscreen, and then reengage the system at random screen locations.

Question 5

Summarize Fitts’ Law

Answer 5

The time it takes to hit a target is a function of the size of the target and the distance to that target.

Question 6

What does Fitts law determine?

Answer 6

The size and location of a screen object

Question 7

What are the three essential parts to Fitts law?

Answer 7

Index of Difficulty (ID)
Movement Time (MT)
Index of Performance (IP)

Question 8

Describe the Index of Difficulty

Answer 8

This value quantifies the difficulty of a task based on width and distance

Question 9

Describe Movement Time

Answer 9

This value quantifies time taken to complete a task based on the difficulty of the task and two empirically derived coefficients that are sensitive to the specific experimental conditions such as type of input device.

Question 10

Describe Index of Performance

Answer 10

This value is based on the relationship between the time it takes to perform a task and the relative difficulty of the task.

Question 11

What are the limitations of Fitts’ Law?

Answer 11

• There is no consistent way to deal with errors.
• It only models continuous movements
• It is not suitable for all input devices
• It doesn’t address two-handed operations
• It doesn’t consider differences between motions away or toward body
• It does not address cognitive functions

Question 12

What are the implications of Fitts’ Law?

Answer 12

• Large targets, and small distances between targets are advantageous
• screen elements should occupy as much of the available screen space as possible
• The largest Fitts’-based pixel is the one under the cursor
• screen elements should take advantage of the screen edge wherever possible
• large menus are easier to use than other types of menus