But Cheap and his colleagues had no such miraculous device. They were forced instead to rely on “dead reckoning”—a process using a sandglass to estimate time, and a knotted line dropped in the sea to approximate the ship’s speed. The method, which also incorporated intuition about the effects of winds and currents, amounted to informed guesswork and a leap of faith. Too often for a commander, as Sobel put it, “the technique of dead reckoning marked him for a dead man.”
