What is Changing Line?

A line that is in the process of transforming from yang to yin or vice versa. When a hexagram contains changing lines, it produces a second (transformed) hexagram. Changing lines are the engine of Liu Yao analysis — they generate, control, or interact with other lines to shape the reading's dynamics.

Source: Bushi Zhengzong (卜筮正宗), Wang Hongxu, 1709