The Zhonglü tongkao 鐘律通考 "Thorough Investigation of the Bell Pitchpipes"
is a book on musical tuning written by the Ming period 明 (1368-1644) scholar Ni Fu 倪複, courtesy name Ni Ruxin 倪汝新, who came from Yinxian 鄞縣 (modern Ningbo 寧波, Zhejiang). His 6 juan "scrolls" long book is divided into 27 chapters that describe all matters of music from a description of the twelve pitchpipes to concrete melodies to songs from the Confucian Classic Shijing "Book of Songs". The arrangement of the book is not done very well, and it might be that copyists are responsible for inconsistencies in the presentation of chapters. The book is accompanied by a preface written by Zhang Bangqi 張邦奇 in 1526, where it is said that the author relied largely on the rules and customs transmitted from the past. Yet is can be seen that in many points the quotations in the Zhonglü tongkao deviate from the original texts, be it statements by Cai Yuanding 蔡元定 (Lülü xinshu 律呂新書), or Zhu Xi 朱熹. In spite of all these consistencies it is included in the imperial reprint series Siku quanshu 四庫全書.
Source: Li Xueqin 李學勤, Lü Wenyu 呂文鬰 (1996). Siku da cidian 四庫大辭典, Changchun: Jilin daxue chubanshe, vol. 1, p. 622.