From the show's conception, they wanted Charlie to use real math. In the pilot, he writes equations to zero in on a serial rapist's residence, based on the geographical pattern of his strikes. Called "geoprofiling," this is a real-world technique developed by Texas State University professor Kim Rossmo. To describe geoprofiling, Charlie uses the metaphor of a lawn sprinkler. If you knew where several drops of water from the sprinkler fell, he explains, you could write equations that showed where the sprinkler is. So if you know where the rapist strikes, you can eventually determine where he lives. As Charlie speaks, equations appear in a scrawl on the margins of the screen, and in the main image the audience sees a real lawn sprinkler. Slow-motion drops of water arc through the air, and when they land, they morph into spots on a map. Finally, we move back to the sprinkler, which has become the location of the killer's home. This is the first example on the series of what the show's creators call "audience visions," and it's pretty cool. But come on. Math lectures? On prime-time television?