Keystroke-Level Model (KLM)
Predicts how long an expert takes on a task by adding up standard action times.
T = ΣK + ΣP + ΣB + ΣH + ΣM
Worked example: M + P + 2B = 1.35 + 1.1 + 0.2 = 2.65 s.
Why it matters
You can compare designs on paper before building anything.
The essentials
- K: press a key, about 0.28 s for an average typist.
- P: point with a mouse, about 1.1 s.
- B: press or release a mouse button, about 0.1 s.
- H: move a hand between keyboard and mouse, about 0.4 s.
- M: mentally prepare, about 1.35 s.
How to use it
- List every action in the task.
- Add the operator times.
- Compare two designs, rather than trusting one number.
Example
Thinking, pointing and clicking once takes about 1.35 + 1.1 + 0.2 = 2.65 seconds.
Watch out
It models skilled, error-free use, not first-time users.