"The Rhythm of the Bamboo Pipe adjusts the Years" - Thousand Character Classic 千字文 – Line 4

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闰余成岁, 律吕调阳。
rùn yú chéng suì, lǜ Lǚ tiáo yáng。

闰 (intercalary) 余 (extra) 成 (turn into) 岁 (year)

Intercalary means inserting days or months into a calendar to make it correspond with a solar year. Ancient writings such as the 史记 Shǐ Jì (“Historical Records”) by 司马迁 Sīmǎ Qiān (c. 163-85 B.C.) have records showing how the lunar calendar was formed based on the cycle of the moon which consists of 355 ¼ days. This was shorter than the 365 ¼ days of the solar calendar. Thus intercalary days and months were introduced to adjust the lunar calendar to correspond with that of the solar calendar. The Chinese usually add an intercalary month to one out of three years to balance. This is what is meant by the above phrase.

律吕 (bamboo pitch-pipe) 调 (adjust) 阳 (Yang)

律吕 lǜlǚ is a musical instrument made from bamboo that has 12 pitch pipes of different lengths. Peng Fasheng in his notes state that “Ranging from low to high, the odd pitch pipes are called 律 lǜ and believed to represent Yang force, the even ones called 吕 Lǚ and believed to reflect Yin energy. They correspond to the twelve months of the year.” Thus, the phrase means the bamboo pitch-pipe is used to adjust or harmonize Yin and Yang. Evelyn Lip suggest that “all principles be they laws of justice or the laws of nature, are regulated in both negative and positive rhythms to achieve harmony, just like musical notes and rhythms.”

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