This paper describes a theoretical model for stages in the cognitive comprehension of a machine from diagrams and accompanying text. From this model, the article discusses the process of designing hypermedia manuals which explain how machines work. Manuals that were based on this model were evaluated in a set of experiments. The authors' conclusions focused on the fact that hypermedia did not show any distinct advantages over print media, but diagrams assist in conveying conceptual ideas and should be accompanied by textual explanations.
