ABSTRACT
This chapter illustrates how the Keystroke-Level Model can be used, both to exploit its possibilities and to work within its restrictions. It also considers an exploratory experiment, in which the detailed performance record of one user was compared to the model's predictions. The Keystroke-Level Model provides a set of heuristic rules for placing M's in a physical encoding to obtain the cognitive encoding. M operations represent acts of mental preparation for applying physical operations. Their occurrence does not follow directly from the physical encoding, but from the specific knowledge and skill of the user. The Keystroke-Level Model most closely corresponds to Model K1 in the goals, operators, methods, and selection rules for the methods family of models. To determine how well the Keystroke-Level Model predicts actual performance times, an experiment was run in which calculations from the model were compared against measured times for a number of different tasks, systems, and users.
