To Become a Sage, especially in a format that allows the powerful search function of contemporary word processing programs, is an extraordinary source for scholars, and particularily for graduate students grappling with the Neo-Confucian tradition, especially in its Establishment, Ch'eng-Chu form. Ch'eng-Chu discourse is heavily laced with phrases that reference not only well-known classical sources but also the extended body of discussion and controversy directly and indirectly relating to those texts. Work in primary sources often involves hours and days trying to run down the original locus of a discussion or the source of what was for the Ch'eng-Chu school a common-place saying or phrase.
Because it aims to present a synoptic view of the entire scope of the Ch'eng-Chu Neo-Confucian vision utilizing as its material its major reference points, the Ten Diagrams is a fabric woven from the main threads of Neo-Confucian discourse. The Commentary takes up many of those threads, which can be easily spotted by scanning the headings listed in the Table of Contents. The Notes are a mine of references to the sources of the most commonly repeated phrases, sayings, and classical references in Ch'eng-Chu metaphysics/cosmology, psychology, and theory of self-cultivation. The Index is rich in the categories and subcategories of the entire discourse. While you might not want to download the whole book, the notes and index are relatively small files and would be a good quick reference for short biographies of major Ch'eng-Chu thinkers in China and Korea and to locate sources and references on major Ch'eng-Chu topics.
These are, of course, the rudiments of the scholarly apparatus of any monograph. I draw special attention to them here because the extraordinary scope of T'oegye's project in composing the Ten Diagrams makes the scholarly apparatus of this book exactly the kind of thing I longed for when I was myself trying to find my way into the heavily textured conversation among Neo-Confucian literati.