The engineer's grin was wider than the remark seemed to require.

"All right," said Cameron tiredly. "Suppose you tell me why sabotage is so unlikely."

"Well," explained the gravital engineer, "it would have to be someone living here, and he wouldn't like it if he suddenly got double or triple gravity or maybe none at all. But there's another reason. Now take a gravital unit. Any gravital unit. Most people think of it as just that—a unit. It isn't really that at all. It has three parts.

"One part is a power source that can be anything as long as it's big enough. Our power source is a nuclear pile, buried deep in the asteroid. You'd have to take Handicap Haven apart to get to it. Part two is the gravital coil, which actually produces the gravity and is simple and just about indestructible. Part three is the gravital control. It calculates the relationship between the amount of power flowing through the gravital coil and the strength of the created gravity field in any one microsecond. It uses the computed relationship to alter the power flowing through in the next microsecond to get the same gravity. No change of power, no gravity. I guess you could call the control unit a computer, as good a one as is made for any purpose."