A scale is rarely included and the positioning and shape of the organs is often inaccurate To get the students started they are told that the heart is approximately the same size as the fist. This gives them a reference point from which they can work out a scale from more abstract diagrams. When they see a liver in a diagram they can then work out how big it is relative to the heart in that diagram, and get an approximation of its actual size. A lot of learning is involved in the selection of appropriate models and the development of dissatisfaction with models that are too simple is of great value to students. Eventually students will pick out the most sophisticated model that they understand and can use. something which many students find very frustrating at first is the idea that there is often no single right answer. They expect there to be a correct colour and a perfect shape for each organ. They should be encouraged to realize that what they are working on is their interpretation of the many different models they see in books and on videotapes