ABSTRACT
Although it is widely accepted that people's ability to use an interactive device depends in part on their having access to some sort of a mental model (e.g., Moran, 1981a), the notion of the "user's conceptual model" (UCM) remains a hazy one, and there are probably as many different ideas about what it might be as there are people writing about it. The common ground covers something like a more or less definite representation or metaphor that a user adopts to guide his actions and help him interpret the device's behavior. The purpose of this chapter is to help clarify the notion of a UCM by examining the mental models appropriate for a number of different designs of pocket calculator.
