"Nothing wrong," said the engineer soothingly. "You get fluctuations while one generator is running. You get a gravity surge when one generator is supposed to drop out but doesn't. The companion machine adds to it, that's all." "They're supposed to be that way? Overlapping so that for a time we have Earth or Earth and a half gravity?" "Better than having none," said Vogel with heavy pride. "Used to happen quite often, before I came. You can ask any of the old timers. I fixed that though." He didn't like the direction his questions were taking him. "What did you do?" he asked suspiciously. "Nothing," said the engineer uncomfortably. "Nothing I can think of. I guess the machines just got used to having me around." There were people who tended to anthropomorphize anything they came in contact with and Vogel was one of them. It made no difference to him that he was talking about insensate machines. He would continue to endow them with personality. "This is the best you can say, that we'll get a wild variation of gravity, sometimes none?" "It's not _supposed_ to work that way but nobody's ever done better with a setup like this," said Vogel defensively. "If you want you can check the company that makes these units." "I'm not trying to challenge your knowledge and I'm not anxious to make myself look silly. I do want to make sure I don't overlook anything. You see, I think there's a possibility of sabotage." The engineer's grin was wider than the remark required. Cameron swiveled the chair around and leaned on the desk. "All right," he said tiredly, "tell me why the idea of sabotage is so funny." "It would have to be someone living here," said the big engineer. "He wouldn't like it if it jumped up to nine G, which it could. I think he'd let it alone. But there are better reasons. Do you know how each gravity unit is put together?" "Not in detail." The gravity generating unit was not a unit. It was built in three parts. First there was a power source, which could be anything as long as it supplied ample energy. The basic supply on the asteroid was a nuclear pile, buried deep in the core. Handicap Haven would have to be taken apart, stone by stone, before it could be reached. Part two were the gravity coils, which actually originated and directed the gravity. They were simple and very nearly indestructible. They could be destroyed but they couldn't be altered and still produce the field. The third part was the control unit, the real heart of the gravity generating system. It calculated the relationship between the power flowing through the coils and the created field in any one microsecond. It used the computed relationship to alter the power flowing in the next microsecond to get the same gravity. If the power didn't change the field died instantly. The control unit was thus actually a computer, one of the best made, accurate and fast beyond belief.