《太平广记·卷二百二十六·伎巧二》
杯里面没有盛酒，杯呈倾斜状；盛上半杯酒时，杯子平正；酒盛满杯后，杯子自动倾翻，将酒倒入池中。
虚则欹，中则平，满则覆。则鲁庙所谓侑坐之器也。
When there is no wine in the cup, the cup is tilted; when half a cup of wine is poured into it, the cup is level; when the cup is full, the cup automatically tips over, pouring the wine into the pool.