The keystroke-level model is a simplified version of GOMS that predicts times for errorfree expert performance of tasks by summing up the times for
keystroking, pointing, homing, drawing, thinking, and waiting for the system to
respond. Card, Moran, and Newell describe an idealized model human proces-
sor whose activity displays the essential features of user behavior. However,
critics complained that these models concentrate on expert users and error-free
performance and place insufficient emphasis on learning, problem solving,
error handling, subjective satisfaction, and retention.