Ergonomics is a multidisciplinary subject and in order for it to be applied in a consistent and coherent way, a model or framework is required which specifies its areas of application, boundaries, and limitations. Such a framework cannot be derived from the study of anatomy, psychology, or physiology alone since these sciences are focused at the level of the human component rather than the human as part of a worksystem. Several attempts have been made to describe the role of the human component in worksystems with varying degrees of success (some of these are presented in later chapters). The most appropriate for the present introductory discussion is derived from the empirical model Leamon (1980). Leamon's human-machine model is compatible with the works tems framework presented here and has the advantage of providing a closer analysis of interactions between the human component and the rest of the worksystem. The