Sailors originally measured the speed of their ships by throwing a literal piece of wood tied to a rope off the back of the boat and counting how many knots in the rope slipped through their hands.

A closer look

Sailors originally measured the speed of their ships by throwing a literal piece of wood tied to a rope off the back of the boat and counting how many knots in the rope slipped through their hands. A sailor would use an hourglass to time exactly how many evenly spaced knots unspooled into the water, which provided a rough estimate of their nautical speed. This incredibly primitive method from the seventeenth century is the entire reason we still use the term knots to describe marine and aviation speeds today. It is wonderfully absurd that modern nuclear submarines and supersonic fighter jets still measure their velocity using terminology derived from a guy tossing a log overboard and staring at sand falling through a glass