Regarding HeTu (河图)

HeTu (河图) is divided into 3 layers:

1, 2, 3 & 4 are known as producing numbers (生数) and they form the inner arrangement. Inner is Yin therefore it represent a ‘form’ a ‘body’

6, 7, 8 & 9 are known as forming numbers (成数) and they form the outer arrangement. Outer is Yang therefore it represents the ‘formless’ Qi and in layman’s terms it is known as force field, energy or aura.

5 resides in the kernel and is the separation distance between producing and forming → e.g. 1 (producing) + 5 (kernel) = 6 (forming).

As such, this draws the distinction between inner and outer arrangement, which gives rise to an important concept where the inner (阴) and outer (阳) arrangements are used separately (生成分用).