This research aims to analyze the different functions of cai, qi and fen applied in the greater carpentry of the Yingzao fashi the oldest complete Chinese architectural manual first issued in 1103, the Song dynasty. Instead of using the units for actual measurement such as zhang, chi, cun, fen and li, cai, qi and fen, three unique modules for measurement are adopted in the greater carpentry.
With a focus on this point, 48 items specified in the greater carpentry are regrouped up to clarify that fen works differently from cai and qi. It is supposed that fen is used for detail dimensions, while cai and qi are used for the structural design.