Departing from the traditional 'annals and biographies' format, Sima Guang adopted a chronological style (編年體; biānniántǐ). This approach presents history as a continuous year-by-year account, facilitating a clearer understanding of cause and effect across events and dynasties.
Sima Guang articulated his reasoning in a memorandum to the Emperor:
"Since I was a child I have ranged through histories. It has appeared to me that in the annal-biography form the words are so diffuse and numerous that even an erudite scholar who reads them, again and again, cannot comprehend and sort them out. ... I have constantly wished to write a chronological history roughly in accordance with the form of the Tso-chuan (左傳), starting with the Warring States and going down to the Five Dynasties, drawing on other books besides the Official Histories and taking in all that a ruler ought to know—matters which are related to the rise and fall of dynasties and connected with the joys and sorrows of the people, and of which the good can become a model and the evil a warning."