Justin Oster

“So no eye chart would be carried aboard. Instead, on a vacant plot of land forty miles north of Laredo, Texas, NASA groundsmen would flatten and rake eight squares of terrain—two thousand feet long to a side each—and cover portions of the squares with either white Styrofoam or dark turf. The astronauts would have to describe the pattern of the alternating dark-light squares as they flew overhead, a pattern that could be switched up every time the spacecraft passed over Laredo. Let the flyboys try to cheat on that one.”
― Jeffrey Kluger, Apollo 8: The Thrilling Story of the First Mission to the Moon