In Pre-Calculus courses, students are taught the composition and combination of functions to model physical applications. However, when combining two or more functions into a single more complicated one, students may lose sight of the physical picture which they are attempting to model. A block diagram, or flow chart, in which each block represents a constituent equation, can present a more understandable picture of the overall process being modeled. This note presents two example problems, a speedometer and a radio station, using block diagrams to represent composition and combination of functions. The TI-84 graphing calculator is referenced. The author has found this approach often helps students better visualize and understand the equations as part of a system. (Contains 11 figures.)