The line that you drew -- the time-temperature curve -- is a picture of what happened during the experiment.
You could also have written down your temperature readings as numbers on a scrap of paper. But a graph gives you a picture that is easier to understand. Can you tell what happened in this experiment by looking at the graph?
You can see that the temperature rose steadily for a period of time, up to a certain point, then the termperature fell. The shape of the graph and the slope of the lines tells the story of the experiment.
So if you're trying to compare this stage of the Energy House witha different stage, you want to compare the graphs of the experiments. You want to put the graphs together.