On the Expansion and Contraction of Earlier and Later Heaven

The numbers of the Earlier Heaven are taken from Qian one through Kun eight. But how are the numbers of Heaven and Earth derived?

Forty-five serves as the center; the calculation is centered and upright. Earlier Heaven is so called because it reveals the subtle; therefore it takes the center, and its numbers root in nine and transform.

-2.5 -3.5 0.5
-1.5      1.5  
-0.5 3.5  2.5

If gains and losses are halved, this becomes even clearer; what is removed is four point five, divided into yin and yang halves, so the total is nine.

According to the Later Heaven, removing five gives:

-1 +4 -3
-2    +2
+3 -4 +1

Thus what Earlier and Later Heaven encompass can be divided into eighteen in yin and yang; for what they advance is not a single number, but half a number.