He had learned his trade where the answer was always to add one more circuit in increasing complexity. Now he had to think of the simplest possible similarity computer. Electronics was out, obviously. He tried to design a set of cams, like the tide machine, to make multiple tracings on paper similar to a continuous horoscope, but finally gave it up. They couldn't build the parts, even if there had been time. He had to depend on what was available, since magic couldn't produce any needed device and since the people here had depended on magic too long to develop the other necessary skills. When only the broadest powers of magic remained, they were hopeless. Names were still potent, resonance worked within its limits, and the general principles of similarity still applied; but those were not enough for them. They depended too heavily on the second great principle of contagion, and that seemed to be wrapped up with some kind of association through the signs and houses and the courses of the planets. He found himself thinking in circles of worry and pulled himself back to his problem. Normally, a computer was designed for flexibility and to handle varying conditions. This one could be designed to handle only one set of factors. It had to duplicate the courses of the objects in their sky and simulate the general behavior of the dome. It was not necessary to allow for all theoretical courses, but only for the normal orbits. And finally he realized that he was thinking of a model--the one thing which is functionally the perfect analogue. It brought him back to magic again. Make a doll like a man and stick pins in it--and the man dies. Make a model of the universe within the sky, and any changes in that should change reality. The symbol was the thing, and a model was obviously a symbol. He began trying to plan a model with three thousand stars in their orbits, trying to find some simple way of moving them. The others watched in fascination. They apparently felt that the diagrams he was drawing were some kind of scientific spell. Ser Perth was closer than the others, studying the marks he made. The man suddenly pointed to his computations. "Over and over I find the figure seven and the figure three thousand. I assume that the seven represents the planets. But what is the other figure?" "The stars," Hanson told him impatiently. Ser Perth shook his head. "That is wrong. There were only two thousand seven hundred and eighty-one before the beginnings of our trouble." "And I suppose you've got the exact orbits of every one?" Hanson asked. He couldn't see that the difference was going to help much. "Naturally. They are fixed stars, which means they move with the sky. Otherwise, why call them fixed stars? Only the sun and the planets move through the sky. The stars move with the sky over the world as a unity."