Smithsonian National Postal Museum

This guide to the Smithsonian National Postal Museum in Washington, D.C. tells the story of William Robey, a collector who bought a sheet of America's new airmail stamp at a Washington post office counter in May 1918 and noticed something the clerk had missed: the biplane printed upside down. You'll hear how postal inspectors tried to buy the sheet back, how it passed quickly from one dealer to the next, and how collectors later numbered every stamp on it to track where each one went. It ends at the case in front of you, holding pieces of that very sheet.