William Gibson & Bruce Sterling – The Difference Engine (1990)
Tobias plucked up the cards, dropped them through a slot, and pulled a bell-rope. There was a sharp clanging. In a moment a clacker arrived for the cards.
“Now what” Mallory said.
“We wait for it to spin through,” the boy said.
“It always takes twice as long as you think,” the boy said, settling back in his chair. “Even if you double your estimate. Something of a natural law.”