The engineer rubbed his chin. "Now I guess you can see why it doesn't always behave as we want it to." He looked questioningly at Cameron, expecting a reply. "I'm afraid I can't," said the doctor. "If it was one of your patients you'd understand," said Vogel. "Fatigue. The gravity control unit is an intricate computer and it gets tired. It has to rest an hour and a half to do forty-five minutes work. It can't keep running all the time any more than any delicate machine can. It has to be shut down to clear the circuits. "Naturally they don't want anyone tinkering with it. It's sealed and non-repairable. Crack the case open and it disintegrates. But first you've got to open it. Now I know that it can be done, but not without a lot of high-powered equipment that I could detect if it was anywhere on the asteroid." In spite of the engineer's attitude it didn't seem completely foolproof. But Cameron had to admit that it was probable none of the accidentals could tamper with it. "I'll forget about gravity," he said. "Next, what about hand weapons? What's available?" "Nothing. No knives even. Maybe a stray bar or so of metal." Vogel scratched his head. "There is something that's dangerous though. I dunno whether you could classify it as a weapon." Cameron was instantly alert. "If it's dangerous someone can find a way to use it. What is it?" "The asteroid itself. Nobody can physically touch any part of the gravity system. But I've often wondered if an impulse couldn't be squeezed into the computer. If anybody can do that he can change direction of the field." Vogel's voice was grave. "Somebody could pick up Handicap Haven and throw it anywhere he wanted. At Earth, say. Thirty miles in diameter is a big hunk of rock." This was the kind of information Cameron had been looking for, though the big engineer seemed to regard the occasion as merely a long overdue social call. "What's the possibility?" Vogel grinned. "Thought I'd scare you. Used to wake up sweating myself. Got so bad I had to find out about it." "Can or can't it be done?" demanded the doctor. "Naw. It's too big to take a chance with. They got monitors set up all over, moons of Jupiter, Mars, Earth, Venus. This or any other gravity computer gets dizzy, the monitor overrides it. If that fails they send a jammer impulse and freeze it up tight. It can't get away until the monitor lets loose." Cameron's mind was already busy elsewhere. Vogel was loquacious and would talk all night if encouraged. It wasn't that he lacked information but he had no sense of what was important. "You don't know how you've helped me," the doctor said, standing up. "We'll have to get together again."