At one end, the cart was attached to a rope with a hanging weight; at the other end to a rope with a weight that floated on the surface of a water reservoir that was drained at a regular pace. Each hour one of the doors opened; at the same time a metal ball was dropped into one of the twelve brass bowls. The rafters sticking out of the building above the doors (identical to the rafters of the Bou Inania Madrasa) supported a small roof to shield the doors and bowls.[3]