"Zi Zhi Tong Jian Kao Yi", referred to as "Tong Jian Kao Yi", is a "by-product" of Sima Guang's compilation of "Zi Zhi Tong Jian", with thirty volumes. This book uses documentary evidence, physical evidence, collation and other methods to correct the authenticity. The conclusions are often "I will follow it now", "I will follow it now", "I will not take it now", "I will leave it now", etc.
In order to "make readers clearly understand the pros and cons of the records and avoid any confusion", while compiling "Tongjian", Sima Guang "referred to a group of books, commented on their similarities and differences, and "Gui Yi Tu" was compiled into 30 volumes of "Zi Zhitong Supervisor Kao Yi" (hereinafter referred to as "Kao Yi"). This book is arranged in the chronological order of "Tongjian" and has 2977 entries. The book is rich in content, including Sima Guang's research on major historical events, places, times, and historical figures in the process of writing "Tongjian".