Formal Action Analysis

This technique is used to make accurate predictions of the time it takes a skilled user to perform a complete task. It uses the following table:

physical movements
Enter one keystroke on a standard keyboard
A skilled typist requires less time, a bad typist may require more than a whole second.
.28 sec
Use mouse pointer to point at object on screen 1.5 sec
Move hand to pointing device or function key
The time to move to or from the mouse is longer than to move to a function key.
.3 sec
visual perception
Respond to a brief light
This varies from .05 sec to .2 sec depending on the intensity of the light.
.1 sec
Recognize a 6 letter word .34 sec
Move eyes to new location on screen .23 sec
mental actions
Retrieve a simple item from long-term memory
Such items are common abbreviated commands like "ls", or a user's password. Retrieving the same item again a few moments later requires only half this time.
1.2 sec
Learn a single "step" in a procedure
This figure is used to estimate how long it takes to learn to perform the task. Some (bright?) people need only 10 to 15 seconds, but no less.
25 sec
Execute a mental "step"
The times may vary a lot because there are very different mental steps.
.075 sec
Choose among methods
This ranges widely from .06 to 1.8 sec depending on the complexity of factors influencing the decision.
1.2 sec

A careful action analysis may provide estimates that are within 20% of the actual time the users will need to perform the task.

A formal action analysis can be prohibitively expensive. But in some cases, evaluating alternatives to find a design which makes users perform a task 1 second faster may result in tremendous savings if this task is performed billions of times.

To the calculated times you should not forget to add delays caused by the system's performance and response time. Typing for instance slows down when characters are not echoed immediately.

When evaluating a first prototype of the Macintosh, Steve Jobs told the developers that if they could make the Mac boot in 5 seconds less, this would save 50 lives. (This means he estimated that all Macs that would ever be sold would together be booted 20 billion times.)