In a complex system, it is difficult to understand how the system works in order to analyse, manage, or improve it. A common solution to overcome this difficulty is to construct a model of the system. A model should be more than a diagram illustrating components of the system and how they are connected. The real purpose of a model is to represent the essential characteristics of something in a way that is amenable to analysis and manipulation. Currently, the leading method to develop a functional model is the Functional Resonance Analysis Method (FRAM). The FRAM provides a way to describe functions that can be used to develop a model of how a system performs. This method is based on four principles: 1) work that goes well and work that doesn’t happen in essentially the same way, 2) performance on all levels of an organization is variable because it must be adjusted to meet existing resources and demands, 3) acceptable and unacceptable outcomes both emerge from variability due to the everyday adjustments, which 4) can lead to functional resonance and non-linear consequences.