Xuan Kong Substitute Divisions and Yuan Long Purity (替卦分金 / 三元龍)
This module supports the substitute-division and bearing-status tools. Each 24-mountain sector is only fifteen degrees wide, so a few degrees of measurement error can move a site from a central 下卦 line into a 兼向 or 替卦 condition. Students learn to treat the line status as a measurement fact before applying any auspicious or inauspicious interpretation.
Three Checks
- Fenjin geometry: record the 120 Fenjin slice and whether the bearing is central, side-line, seam-adjacent, or void-prone.
- Yuan Long purity: identify earth, heaven, or human Yuan Long and avoid mixing a line as though all neighbouring mountains were interchangeable.
- Lineage variant: preserve whether the lesson uses a Shen-style center-nine-degree rule, a stricter three-degree rule, or another declared substitute-star table.
The module's job is to prevent silent chart drift. If a site sits on a boundary, the academy report should show the competing readings and the reason one was selected, rather than smoothing the degree into a false certainty.