What is Line Strength?

The assessment of each line's power based on how the casting month and day branches relate to its Five Element. A line may be Prosperous (旺), Moderate (相), Weak (休), or Dead (死). The same line can be strong in one month and dead in another, which is why Liu Yao requires the exact casting date. The useful spirit's strength is the primary factor in determining a reading's verdict.

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