by Isaac Asimov
“Aub! How much is nine times seven?”
Aub hesitated a moment. His pale eyes glimmered with a feeble anxiety.
“Sixty-three,” he said.
Congressman Brant lifted his eyebrows. “Is that right?”
“Check it for yourself, Congressman.”
The congressman took out his pocket computer, nudged the milled edges twice, looked at its face as it lay there in the palm of his hand, and put it back. He said, “Is this the gift you brought us here to demonstrate. An illusionist?”
“More than that, sir. Aub has memorized a few operations and with them he computes on paper.”
“A paper computer?” said the general. He looked pained.