In this scence, Charlie explains how he used statistical modeling to develop a heatmap of where the killer's home most likely is. He then illustrates how the killer's crime scenes seem randomly distributed, but are not.
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.