Keystroke-level Model - Step Terminology

Step Terminology

Kieras (1993, 2001) defines the following operations:

• K, key press and release (keyboard)

Best Typist (135 wpm) --- 0.08 seconds Good Typist (90 wpm) --- 0.12 seconds Poor Typist (40 wpm) --- 0.28 seconds Average Skilled Typist (55 wpm) --- 0.20 seconds Average Non-secretary Typist (40 wpm) --- 0.28 seconds Typing Random Letters --- 0.50 seconds Typing Complex Codes --- 0.75 seconds Worst Typist (unfamiliar with keyboard) --- 1.20 seconds

• P, Point the mouse to an object on screen --- 1.10 seconds
• B, Button press or release (mouse) --- 0.10 seconds
• H, Hand from keyboard to mouse or vice versa --- 0.40 seconds
• M, Mental preparation --- 1.20 seconds
• T(n), Type string of characters (n * K sec.)
• W(t), User waiting for the system to respond
• D(n0,l0), Draw n0 straight line segment with mouse of total length l0 centimeters

A mouse click would be written "BB" (button press, button release) while a sequence of 3 keyboard key presses is "AAA" or "T(n)" ("T" stands for "type").

A common operation that involves pointing and clicking something on the screen would be written "MPBB" (think, point, press, release).

KLM is not the only technique for evaluating interfaces, but it can be used to compare the speed of two different interfaces designed to accomplish the same task.