The question of what the operator of a dynamic system needs to know was investigated in an experiment using PLANT, a generic simulation of a process. Knowledge of PLANT was manipulated via different types of instructions, so that four different groups were created: 1) Minimal instructions only; 2) Minimal instructions + guidelines for operation (Procedures); 3) Minimal instructions + dynamic relationships (Principles); 4) Minimal instructions + Procedures + Principles. Subjects then controlled PLANT in a variety of familiar and unfamiliar situations. Despite the fact that these manipulations resulted in differences in subjects' knowledge as assessed via a written test at the end of the experiment, instructions had no effect upon achievement of the primary goal of production; however, those groups receiving Procedures controlled the system in a more stable manner. Principles had no apparent effect upon subjects' performance. There was no difference between groups in diagnosis of unfamiliar events.
