This class demonstrates how call graphs are used to quickly see aspects of the system that are difficult, or impossible, to see any other way. Call graphs show the calling relationship among functions in a system. They can be constructed using tools available today. Once constructed, they are used to quickly and concisely determine important system properties such as how much stack space is required, or which functions take up the most time. This class introduces call graphs, shows how to construct them, and gives field tested examples of their usage.