Computer-based multimedia technologies allow designers to construct interactive and animated graphical presentations to communicate dynamic information. The conventional wisdom is that such presentations are more effective than printed materials. This paper presents research that critically examines this assumption. Design guidelines and principles were derived from a cognitive process model of multimodal comprehension. These guidelines and principles were used to create several expository presentations in two domains}the concrete domain of mechanical systems and the abstract domain of computer algorithms. A series of experiments evaluated the efficacy of these presentations and compared them with other kinds of presentations such as books, CD-ROMs and animations. The experiments also compared computer-based interactive graphical presentations and static printed presentations containing the same information. Experimental results suggest that the communicative efficacy of multimodal presentations is more related to their match with comprehension processes than with the interactivity and dynamism of the presentation media. The results support a model-based approach to the design of multimodal expository presentations of dynamic information. The comprehension model and corresponding design guidance should aid designers in building interactive graphical presentations that are more effective than intuitive designs in communicating dynamic content.