Nathan Cooper’s big idea: Print a ruler on a pencil. Why? Because he hated fumbling for one while doing his math homework. But who would listen to an 11-year-old kid? Plenty of people, apparently.

Use a dollar bill to measure. Every piece of US paper money in your wallet/pocket/sock is 6" long. Folded in half, and you have a 3" measuring stick, and so on. I can't tell you the number of times ...