More than 230 years ago, a band of buccaneers raided a ship headed for America—possibly changing the course of U.S. history. The pirates stole scientific models meant to help convince the U.S. government to adopt the metric system—a measuring system with units based on multiples of 10. Today the U.S. is one of the few countries whose road signs list distance in miles rather than kilometers, scales read weights in pounds instead of kilograms, and cartons of milk come in gallons instead of liters. Pirates may be partly to blame.