Understanding Reality: A Taoist Alchemical Classic, by Chang Po-tuan, transl. Thomas Cleary

with a concise Commentary by Liu I-ming

Introduction

1 sixteen verses, representing  the "eight ounzes" of yin and the "eight ounces" of yang, forming "one pound" of elixir

2 Sixty four verses, modeled on the number of signs in the I Ching