This chapter explores a powerful tool for gaining deeper insight into the system in need of improvement by way of a method called "functional analysis". It considers several different functional models as learning aids. Before delving into the details of creating and utilizing functional models, it is necessary to understand the particulars of functional language. The key to functional language is to describe what is actually happening in order to perform the function. To build a functional model, it is necessary to decide upon the components that will go into the model and what those components' relationships are. Another use of functional analysis is to study and apply the concept of system trimming to increase the system's ideality. When converting the interaction graphics to a functional model, it is necessary to assign functional relationships between the components and what the quality of those functions are.