Spiritual practices are rich in imagery and mythological elements. The purpose of which is to aid a practitioner's inner visualization. As explained in my previous post on Wuzhen Pian 悟真篇, such visualizations are fundamentally physical in nature, and therefore they have to work upon one's cultivation of the highest level of morality to reach the ultimate goal of spiritual enlightenment. And for those practices that aim at consolidating one's spiritual strength for selfish personal goals and/or gratifications, classic Taoists would call them "Evil cults" 邪魔外道。 But now let's get back to the main subject of this post: the mathematical-myth of microcosmic circulation.
The mechanism: chi moves up from bottom to top at the back with inhalation and moves down from top to bottom in the front with exhalation.
Definition 1: the 12 Earthly branches are used to signify the equally spaced physical positions (This system was built from observations of the orbit of Jupiter, dividing the celestial circle into 12 sections to follow the orbit of 歳星 Suixing (Jupiter, the Year Star).
Definition 2: The Kan (坎) trigram and the Li (離) trigram from I-Ching (易經) are used to signify the movement or exchange of Yin (broken line) and Yang (solid line). In particular, the middle Yang (solid) line of Kan is to travel to the top with then the middle Yin (broken) line of Li travel to the bottom.
Definition 3: Based on I-Ching, the solid Yang line is represented by number 9, whereas the broken Yin line is represented by number 6. Mathematically a complete circle is divided into 360 degrees (which by definition being a complete 12-year orbit of Jupiter). Taoist definition: one step forward (up or down) is represented by 4.
The mathematical formula is now obvious:
1. Going up : 9 x 4 x 6 = 216
2. Going down: 6 x 4 x 6 = 144
Total= 216 + 144 = 360 (Bravo, we have perfection!)