If it can be said that a ruler is clever, Elsa Werth 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.