Luopan 羅盤 Glossary
The Chinese geomancer's compass: a magnetic needle at the centre of a stack of concentric rings （層） carrying stems, branches, trigrams, dragons and star scales.
Luópán · 罗盘 (simplified) · 羅盤 (traditional)
Source credibility (S/A/B/C/X): S A Rule computability (A/B/C): A C for the "declination fossil" theory
What it is
A luopan is not one scale but many. Around the central heaven pool （天池） with its needle, rings repeat the 24 Mountains in slightly rotated copies — the three "needles" （三針） — and add rings of 72 dragons, 60 dragons, 120 fenjin, the 64 hexagrams and the 28 lunar mansions. Three plate families are recognised: the San He plate （三合盤／楊公盤） built around the three-needle stack, the San Yuan plate （三元盤／蔣盤） built around a single earth-plate correct-needle ring plus the 64-hexagram ring, and the combined plate.
The three needles, stated in absolute degrees (verbal descriptions of their rotation direction contradict each other across sources, so the project only uses degrees): the earth-plate correct needle （地盤正針） places Zi at 352.5°–7.5°; the heaven-plate sewing needle （天盤縫針） places Zi at 0°/360° (correct needle +7.5°); the human-plate middle needle （人盤中針） places Zi at 345° (−7.5°). San He practice uses the middle needle for sand evaluation and the sewing needle for water; Xuan Kong insists on the correct needle alone — Jiang Dahong's commentary is explicit that "the plate method uses only the correct needle; the remaining rings were all added later, in vain".
School differences
The two lineage families genuinely need different hardware. Collated sources show Xuan Kong requires only the heaven pool, the correct-needle 24-mountain ring and the 360° scale (plus the 64-hexagram ring for the Da Gua school), while San He requires the three-needle stack and the dragon, fenjin and mansion rings. Two further disputes touch the luopan directly: some lineages set yin-house facing on the sewing needle rather than the correct needle, and the popular claim that the sewing needle's 7.5° offset is a "fossil" of historical magnetic declination is contradicted by hard declination data (see Magnetic Declination) and is rated C — a belief statement, not a computable rule. Also note: vendor claims of "19-layer San Yuan plates" have no traceable source and must not be quoted; the verifiable figures are the 36-layer San He list and a 22-layer San Yuan list. Background: School Dispute Register.
How this engine computes it
- All plate geometry is expressed in absolute degrees; the three needles are three fixed ring offsets (+7.5° / 0° / −7.5°) over the 24-mountain table.
- The engine separates the plate construction from physics: "three needles" and "magnetic declination correction" are two independent switches, each declaring its own reference north; they are never merged or substituted for each other.
- A magnetic-north / true-north switch applies WMM2025 declination by coordinates and date (see Magnetic Declination).
- Because a phone magnetometer's error (±3°–5° outdoors at best) is comparable to the whole ±4.5° lower-trigram zone, compass input only feeds the 24-mountain layer without off-grid judgements unless a higher-precision method is used.
Related entries
24 Mountains · Xia Gua / Ti Gua · Magnetic Declination · 64 Hexagrams · San Yuan vs San He
Back to the glossary index.