Two bodies initially at different temperatures gathered into an isolated container exchange heat and reach an equilibrium state with a common final temperature. During the process, the system is out of equilibrium and its intermediate temperature is not well defined. By conceiving a quasi-static process with infinitesimal steps from the initial to the final state, a graphic representation of the intermediate temperatures is possible. We imagine an isolated container with the bodies in compartments separated by a wall, as shown in Fig. 1. If the conductivity of the wall is controlled, the heat exchange is made gradually through a sequence of very small portions of heat flowing from one body to the other. Each step is followed by a "dead time" in order to reach a momentary equilibrium state. These graphs are useful for students who need to analyze a phase change.