In this scene, Charlie and Don are trying to come up with equations for finding the killer's home location. Using what Don knows about crime, Charlie then makes equations to reflect this.

This scene illustrates how statistical models (especially concerning human behavior) can be wrong due to a variety of unforeseen factors.

In this scene, Charlie has everyone spread out around the room to illustrate how their distribution is nonrandom due to their lack of clustering.

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 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.