An experiment was carried out to investigate whether it is useful to add system information to procedural information in instructional text. It was assumed that readers of instructions construct both a procedural and a system mental model, and that the latter enables the readers to infer possible missing information in procedural instructions. Moreover, it was assumed that system information would increase the cognitive load during reading and practicing, and that it would affect the appreciation of the instructions as well as the self-efficacy of the reader. The participants in the experiment read instructions and practiced with a fictitious machine before performing a number of tasks and answering a questionnaire. The results indicate that system information increased the cognitive load during reading and decreased self-efficacy, while the instructional text with system information was judged as more difficult. The effect on performance is limited: system information leads to faster performance for correctly completed tasks.

Guidelines and models for procedural instructions can be supported by three types of research. Careful analytical studies of collections of instructions can help to identify, describe, and evaluate strategies that writers and designers apply. Empirical studies measure the effects of document variables on the performance of users, thus offering evidence, contraevidence, or refinements for existing guidelines. Theoretical studies, finally, aim to describe and explain the behavior of readers of instructions. To designers and writers, they provide a deeper insight in the underlying cognitive processes that determine success or failure of their work. This special issue offers research articles in all three categories.

Instructions for operating a control panel were presented in five different formats: flowchart, logical tree, yes/no tree, decision table, and list. Subjects had to choose one out of eight buttons, depending on the settings of the control panel. The results show that the decision table resulted in more errors, and that both the decision table and the list took longer than the three other formats, which did not show mutual differences. It turned out that the subjects valued most the format they had been using, except for those who had worked with the list. It is suggested that the users' ease of orientation for a diagram's format, both during reading and after "switching" between equipment and instructional text, explains the differences between the formats.