The original construction ruler (Yingzao chi) is calculated to be 29.939 centimetres long. It conforms to the long and short ruler system since the Tang and Song dynasties. Each ruler (1 chi) is 10 cun [寸], and each chi is divided into 12 small cun. The construction module was adopted. The basic modulus is 1 chi. 4 small cun is the infra - module, which is 1/3 of the basic modulus. 0.4 small cun is also an infra - module, which is 1/30 of the basic modulus. 30 cun is the multi - module, which is three times the basic modulus of 1 chi. This module is very similar to modern building modules. The building shape is in a proportional relationship under integer - size constraints.