Zula was noticing that the newer circuits all had fuses in them but that several of the sockets for what she took to be fifth-floor apartments were vacant. She reckoned that empty sockets were probably a marker for vacant apartments. To discourage squatters and to prevent other tenants from pirating electricity, they would pull the fuse, thereby shutting off the power, to any unit that was not occupied. Scanning the whole panel, she saw that every floor had at least one or two vacant units but that they were most common on the fifth floor: not surprising since, in a building with no elevator, those were the least desirable apartments.