Extending GOMS 'with if-then rules to describe the conditions and actions in
an interactive text editor proved to be a powerful addition (Kieras and Polson,
1985). The number and complexity of production rules gave accurate predictions of learning and performance times for five text-editing operations: insert,
delete, copy, move, and transpose. Other strategies for modeling interactive-
system usage involve trmlsitioll diagrams (Fig. 2.5). These diagrams are helpful
during design, for instruction, and as a predictor of learning time, performance
time, and errors.