《晋书·志·第六章》
三分损一，下生中吕；京房用三分益一，上生中吕。
三分损一，下生中吕；京房三分益一，上生中吕。
When a third is subtracted, the pitch Chung-lu is produced from below. When a third is added, the pitch Chung-lu is produced from above, according to Jing Fang.