Walk Your Weight

This long plank rests on a pivot, making it a lever you can walk on, and it works as a weighing scale. The marks along it are weights.

The farther you walk from the pivot, the more turning effect (torque) your weight has. The plank tips when your turning effect matches the one on the other side, so a heavier person tips it closer to the pivot and a lighter one has to walk farther. The mark where it tips shows your weight. Old market scales, called steelyards, weigh things the same way.