There's a sign next to a bridge that says "Weight Limit: 10 tons". Calvin asks how they know the limit and his dad says they build the bridge, then drive progressively heavier trucks across it until it falls down. Then they rebuild it exactly how it was and put up the sign for the how heavy the last truck was.

One of my favorites!

https://www.reddit.com/r/calvinandhobbes/comments/u3dqja/how...