A few years ago, when I was visiting my (very) old friend Charlie up in Washington, he gave me what has become a treasured possession.
It looks like a normal, old, wooden ruler. A foot long with inches on one side and centimeters (going the other direction, of course) on the other.
But feast your eyes on it. If you don’t see the problem immediately, that’s normal. Just relax. Take your time. And wonder: how did this happen?
Please don’t give it away in the comments. Be sly 🙂