In Su Song's clock tower, 36 tilting scoops were mounted on a large drive wheel. A steady flow of water filled each of the scoops in turn. When a scoop filled with water, it became heavier than the checking fork and lower balancing lever which supported its weight, and turned downward like the nodding pots used for irrigation in ancient China.
水運儀象台就是在一個大樞輪上，安置了三十六個可傾式受水壺，水流穩定地循序注入各個壺中，當壺水滿，重量大於托住它的槓桿「格叉」與「樞衡」時，受水壺就會像古代的敧器一樣，向下翻轉。