If it can be said that a ruler is clever, they think this one qualifies. French visual artist Elsa Werth’s intervention on this engraved metal ruler is simple but transformative, like all the best solutions. She placed a mathematical operator in between each number and the product of this sequence—once added, subtracted, multiplied and divided—is equal to the actual length of the ruler: 30 cm on one side, 12 inches on the other.