Likewise, while the fridges didn't contain food, they held large containers filled with water, to simulate the thermal mass and humidity of an appropriately stocked refrigerator. This obsession with accurate levels of ambient moisture and seemingly minor sources of heat and cold is what differentiates the Campbell Creek project from a more general study, conducted by flesh and blood participants. When you can control exactly how much simulated sweat, breath and body heat is trickling into the environment, there's no need to apply a margin of error to your resulting conclusions. “While we don't have humans in the home, we do have a better representation—a more consistent representation—of humans,” says Roderick Jackson, an ORNL researcher and program manager for the Campbell Creek project. Again, these house are pretending in perfect unison, with no variation. It's a rare case of robotic systems—or automated systems, to be more accurate—being preferable to the humans they're emulating.