According to Kuo Mei-fang's research, Su Song solved this problem by using a system of balanced levers as an escapement, to alternately check and release the drive wheel: When a full scoop tilted down and struck the trip lever, a connecting rod joined to the trip lever pulled sharply downwards on the weighted end of the upper balance lever.
根據郭美芳研究，蘇頌當年是用一座一卡一放的擒縱裝置﹘﹘「天衡」，來解決這個問題：