"Suit yourself, tin boy. I don't care whether you believe it or not."
Again there was a twittering of code. Then: "Stand aside, please."
Mitch stepped out of the doorway. The subunit bounced over the threshold with the aid of the four-footed sprockets and clattered hurriedly toward the library. Mitch followed, grinning to himself. Despite Central's limitless "intelligence," she was as naive as a child.
He lounged in the doorway to watch the subunit fiddling with the dials of the safe. He motioned the girl down, and she crouched low in a corner. The tumblers clicked. There was a dull snap. The door started to swing.
"Just a minute!" Mitch barked.
The subunit paused and turned. The machine gun exploded, and the brief hail of bullets tore off the robot's antenna. Mitch lowered the gun and grinned. The cop just stood there, unable to contact Central, unable to decide. Mitch crossed the room through the drifting plaster dust and rolled the robot aside. The girl whimpered her relief and came up out of the corner.
The cop was twittering continually as it tried without success to contact the Coordinator. Mitch stared at it for a moment, then barked at the girl, "Go find some tools. Search the garage, attic, basement. I want a screwdriver, pliers, soldering iron, solder, whatever you can find."
She departed silently.
Mitch cleaned out the safe and dumped the heaps of papers, money, and securities on the desk. He began sorting them out. Among the various stacks of irrelevant records he found a copy of the original specifications for the Central Coordinator vaults, dating from the time of installation. He found blueprints of the city's network of computer circuits, linking the subunits into one. His hands became excited as he shuffled through the stacks. Here were data. Here was substance for reasonable planning.
Heretofore he had gone off half-cocked and quite naturally had met with immediate failure. No one ever won a battle by being good, pure, or ethically right, despite Galahad's claims to the contrary. Victories were won by intelligent planning, and Mitch felt ashamed of his previous impulsiveness. To work out a scheme for redirecting Central's efforts would require time. The girl brought a boxful of assorted small tools. She set them on the floor and sat down to glower at him.
"More cops outside now," she said. "Standing and waiting. The place is surrounded."
He ignored her. Sarquist's identifying code-it had to be here somewhere.
"I tell you, we should get out of here!" she whined. "Shut up."
Mitch occasionally plucked a paper from the stack and laid it aside while the girl watched.
"What are those?" she asked.
"Messages he typed into the unit at various times." "What good are they?"
He showed her one of the slips of yellowed paper. It said: Unit 67-BJ is retired for repairs. A number was scrawled in one corner: 5.00326.
"So?"
"That number. It was his identifying code at the time." "You mean it's different every day?"
"More likely, it's different every minute. The code is probably based on an equation whose independent variable is time and whose dependent variable is the code number."
"How silly!"
"Not at all. It's just sort of a combination lock whose combination is continuously changing. All I've got to do is find the equation that describes the change. Then I can get to Central Coordinator."
She paced restlessly while he continued the search. Half an hour later he put his head in his hands and gazed despondently at the desk top. The key to the code was not there.
"What's the matter?" she asked.
"Sarquist. I figured he'd have to write it down somewhere. Evidently he memorized it. Or else his secretary did. I didn't figure a politician even had sense enough to substitute numbers in a simple equation."
The girl walked to the bookshelf and picked out a volume. She brought it to him silently. The title was Higher Mathematics for Engineers and Physicists.
"So I was wrong," he grunted. "Now what?"
He shuffled the slips of paper idly while he thought about it. "I've got eleven code numbers here, and the corresponding times when they were good. I might be able to find it empirically."
"I don't understand."
"Find an equation that gives the same eleven answers for the same eleven times, and use it to predict the code number for now."
"Will it work?"
He grinned. "There are an infinite number of equations that would give the same eleven answers for the same eleven substitutions. But it might work, if I assume that the code equation was of a simple form."
She paced restlessly while he worked at making a graph with time as the abscissa and the code numbers for ordinates. But the points were scattered across the page, and there was no connecting them with any simple sort of curve. "It almost has to be some kind of repeating function," he muttered, "something that Central could check by means of an irregular cam. The normal way for setting a code into a machine is to turn a cam by clock motor, and the height of the cam's rider is the code number for that instant."
He tried it on polar coordinates, hoping to get the shape of such a cam, but the resulting shape was too irregular to be possible, and he had no way of knowing the period of the repeating function.
"That's the craziest clock I ever saw," the girl murmured. "What?" He looked up quickly.
"That electric wall clock. Five minutes ahead of the electric clock in the living room. But when we first came it was twenty minutes ahead."
"It's stopped, maybe."
"Look at the second hand."
The red sweep was running. Mitch stared at it for a moment, then rose slowly to his feet and walked to her side. He took the small clock down from its hook and turned it over in his hands. Then he traced the cord to the wall outlet. The plug was held in place by a bracket so that it could not be removed.
The sweep hand moved slowly, it seemed. Silently he removed the screws from the case and stared inside at the works.
Then he grunted surprise. "First clock I ever saw with elliptical gears!"
"What?"
"Look at these two gears in the train. Ellipses, mounted at the foci. That's the story. For a while the clock will run faster than the other one. Then it'll run slower." He handled it with growing excitement. "That's it, Marta-the key. Central must have another clock just like this one. The amount of lead or lag-in minutes-is probably the code!"
He moved quickly to the direct-contact unit. "Tell me the time on the other clock!"
She hurried into the living room and called back, "Ten-seventeen and forty seconds…forty-five…fifty-"
The other clock was leading by five and one-quarter minutes. He typed 5.250 on the keyboard. Nothing happened. "You sure that's right?" he called.
"It's now ten-eighteen-ten… fifteen…twenty."
The clock was still slowing down. He tried 5.230, but again nothing happened. The unit refused to respond. He arose with an angry grunt and began prowling around the library. "There's something else," he muttered. "There must be a modifying factor. That clock's too obvious anyway. But what else could they be measuring together except time?"
"Is that another clock on his desk?"
"No, it's a barometer. It doesn't-"
He paused to grin. "Could be! The barometric pressure difference from the mean could easily be mechanically added or subtracted from the reading of that wacky clock. Visualize this, inside of Centraclass="underline" The two clock motors mounted on the same shaft, with the distance between their indicator needles as the code number. Except that the distance is modified by having a barometer rigged up to shift one of the clocks one way or the other on its axis when the pressure varies. It's simple enough."