"Soldiers, right," the old man answered. "The Quipucamayocuna—"
"The what, Dan?"
"Knot officers," explained the other, "kept track of him all. They counted tens, single knot meant ten; double knot, hundred. Now read him. Cross-knotting is for groups."
Eric worked for a quarter of an hour and then looked up.
"I've got it," he said.
"What is he?"
"In this town," said the boy, "there were seven regiments of soldiers, I've got down the exact number of men in each regiment. Some had plenty of food in the regimental storehouse, some had only a little. But—if I get it right—there was money belonging to each regiment in a treasure-house, somewhere, like a bank. I suppose they could exchange this for food. And, if I've read it right, there was one regiment which had money but no men. I suppose they were wiped out in battle."
"Very good," answered the puzzle-maker, looking pleased. "You keep accounts, your own money?"
"Of course," answered the boy, pulling out a little diary from his pocket.
"Here, string," said the old man. "Write your week's accounts in quipu."