The caissons or gondolas always carry a combined weight of of water and boats, with the gondolas themselves each weighing . Care is taken to maintain the water levels on each side, thus balancing the weight on each arm. According to Archimedes' principle, floating objects displace their own weight in water, so when the boat enters, the amount of water leaving the caisson weighs exactly the same as the boat. This is achieved by maintaining the water levels on each side to within a difference of using a site-wide computer control system comprising water level sensors, automated sluices and pumps. It takes to power ten hydraulic motors, which consume per half-turn, roughly the same as boiling eight kettles of water.