They can be simple, like the geometry of a cone or they may involve more sophisticated models for structural analysis, heat transfer, chemical engineering process design or even economics. Others may use spreadsheet. Fortunate ones use TK Solver . They are fortunate because TK helps them set up a model quickly and solve it in many creative ways, to get the best results with time savings of 90 percent or more. The cone model can be set up in TK in minutes, by typing in the equations just the way you see them, without worrying about what will be inputs and outputs.
R is for relationship.
Think of the R-Graph as a replacement for the commonly used flow charts. In the cone model shown, when r and s are inputs, see how the solution propagates. But you can just as easily see what will happen if you input r and q and calculate the rest. The TK model looks at all the relationships simultaneously and comes up with the answers. By the way, you do not have to draw R-Graphs.