In this scene, Charlie explains how the drops of water coming from a sprinkler can be used to extrapolate the sprinkler's location. He then explains how, by modeling what the previous crime scenes have in common, they can determine the killer's home.
In this scene, Charlie explains how he checked the equations he's using to catch the killer by going backwards from his results and making sure he gets the same answer. Because he doesn't, he realizes that either one of his expressions or the data he was given is wrong.
In this scene, Charlie and Don realize that their mathematical model is wrong because they were focusing on the wrong factor (the home) as opposed to the right one (the criminal's workplace).
In this scene, Charlie explains sabermetrics (the math of baseball) to one of his colleagues and explains that he will have to figure out what each part of the expression means.