Read this excerpt from The Great Fire. Several minutes passed before Schaffer looked up from what he was doing and saw flames leaping wildly into the black sky. The light was from a different fire after all; he'd been fooled because this new blaze was almost directly behind the still-flickering remnants of the Saturday October 7 fire.

He studied the flames, trying to determine their exact location. This wasn't easy because of the distance and tall buildings between him and the flames. In addition, the moonless sky was made even murkier by the swirling, smoky haze. Schaffer signaled down the speaking tube and had his assistant strike Box 342. This sent engines rumbling through the streets — to a location almost a mile away from the O'Learys' barn.

What caused Schaffer to instruct his assistant to strike Box 342, accidentally sending firefighters to the wrong place?