What is Xieji Bianfang Shu?

The Imperial Guide to Date Selection and Directional Harmony, a 36-volume compilation commissioned by Emperor Qianlong in 1739. Preserved in the Siku Quanshu (Complete Library of the Four Treasuries). It is the most authoritative classical source for Chinese almanac calculations, systematically cataloging celestial spirits, day types, and activity-specific rules. Six Lines uses this text as the foundation for all almanac computations.

Source: Siku Quanshu (四庫全書), Zi Section, Astronomy/Mathematics