A reference mode is a graphical statement about a problem. Verbally, the problem was stated as "production is less stable than sales." Graphically we might draw:
This reference mode is a sketch of behavior we might expect a model to produce. It might be real data from your records, or your expectation of what might happen in a new situation. The reference mode is used to focus activity. Having mapped out one or more reference modes the goal is to define the simplest structure that is sensibleF_5 and capable of generating patterns of behavior that qualitatively resemble the reference modes. If appropriate, such a structure can also be refined in order to develop a model that can be validated quantitatively against the available data.
