Luopan Compass Layers
A luopan（羅盤，luópán；繁體 羅盤）is not one dial but a stack of concentric rings, each encoding a different school's way of slicing the same 360°. This page describes the ring types that are actually documented — the three-needle core above all — and separates what is attested from what is not.
Reference document · collated against the repository rule tables and compass research · static page, no scripts, no data collection.
A note on ring counts
There is no single canonical number of luopan rings, and any page that quotes one total is quietly choosing a plate type for you. What the sources support is this: the manufacturers' own catalogues say plates run "as few as three rings, as many as forty-plus"; the San He plate is documented with a complete, itemized 36-ring list (the Wu Lu Heng compass house material); and the only concrete ring-by-ring San Yuan list our collation found is a 22-ring list. Beyond those two documented ends, specific totals circulate without a traceable source, so we do not print them. What follows describes ring types, which are what the schools actually disagree about.
The three plate families
| Plate family | Chinese name | Signature rings |
|---|---|---|
| San He plate（Yang Gong / Hui style） | 三合盤（楊公盤／徽盤） | Three 24-Mountain rings — Correct, Center and Seam needle — plus the 72 Dragons, 60 Dragons, 120 Fenjin and the 28 Lunar Mansions |
| San Yuan plate（Jiang plate / Yi plate） | 三元盤（蔣盤／易盤） | A single Earth-plate 24-Mountain ring, plus the 64 Hexagrams (square and round arrangement), the star-assignment rings（挨星）and the two-epoch period system |
| Combined plate | 綜合盤（元合通用盤） | Both of the above merged into one dense plate |
The three needles（三針 sānzhēn；繁體 三針）
The San He plate's defining feature is three copies of the 24-Mountain ring, each rotated by half a mountain against the next. "Half a mountain" is 7.5° — the classical texts call it "half a character"（半個字）— and the middle and seam needles differ from each other by a full "character", 15°. The offsets below are the absolute bearings of the Zi（子 zǐ）mountain on each ring, measured clockwise from true north 0°; this is the only framing all collated sources agree on, because clockwise/counter-clockwise phrasing in the literature is self-contradictory while the absolute numbers are not.
| Ring | Chinese name | Zi mountain spans | Offset vs. Earth plate | Function |
|---|---|---|---|---|
| Earth plate, Correct Needle | 地盤正針 dìpán zhèngzhēn | 352.5°–7.5° | baseline | Sitting/facing determination（立向）, dragon-grading（格龍）, Eight Mansions; used by San He as well as San Yuan |
| Heaven plate, Seam Needle | 天盤縫針 tiānpán fèngzhēn | 0°/360° | +7.5° | Water intake（納水）and the paired-mountain five phases（雙山五行） |
| Human plate, Center Needle | 人盤中針 rén·pán zhōngzhēn | 345° | −7.5° | Sand elimination（消砂／撥砂） |
The Seam Needle's name is its own explanation: each seam-needle mountain sits dead-center on the seam（縫）between two correct-needle mountains — that is exactly what a half-mountain rotation means. Reading outward through the plate, the conventional order is Earth plate innermost, Human plate in the middle, Heaven plate outermost, though the collation notes that individual sources contradict each other on this and a Qing commentator already complained about rings being mounted on the wrong needles.
Disclosed school differences (presented, not voted on): the works 《地理原真》《地理五訣》hold that yin-house sitting should be taken on the outer Heaven-plate Seam Needle, contrary to the majority practice of always using the Earth plate; and some lineages hold the Human plate "is not for sand elimination at all". The needle offsets themselves are the one part every source agrees on.
A common error, corrected
A saying circulates in the trade that "the San Yuan school uses the Center Needle; the San He school uses the Correct Needle". It is backwards. The San Yuan plate — the plate Xuan Kong feng shui is built on — carries only the one Earth-plate Correct Needle ring; it is the San He plate that carries all three needles. Two classical statements pin this down: Jiang Dahong's commentary, "the plate method uses only the Correct Needle; all the other rings were added later, in vain"（盤法只用正針……其餘諸盤層數，皆後人妄添）, and Zhong Yiming's rule that whoever takes sitting or facing on the Human or Heaven plate "cannot be using the Xuan Kong method". Accordingly, Xuan Kong has no use for the Center Needle, the Seam Needle, the 72 Dragons, the 60 Dragons, the 28 Mansions or the 120 Fenjin; the San He system requires all of them.
The rings beyond the needles
Beyond the three needle rings, the documented ring types and their degrees are:
| Ring | Chinese name | Degree division | Notes |
|---|---|---|---|
| Penetrating-Mountain 72 Dragons | 穿山七十二龍 | 5° each (360/72) | The eight stems and four dimensions are left blank — "void"（空亡）positions; only the Geng/Bing/Ding/Xin positions count as "jewel"（珠寶） |
| Penetrating-the-Ground 60 Dragons | 透地六十龍 | 6° each (360/60) | Each of the twelve Branch mountains governs five dragons |
| 120 Fenjin divisions | 一百二十分金 | 5 subdivisions × 3° per mountain | Only the Bing/Geng/Ding/Xin subdivisions are used; Jia/Ren are "orphan-void"（孤虛）, Wu/Ji "tortoise-shell void"（龜甲空亡） |
| 64 Hexagrams, 384 lines | 六十四卦・三八四爻 | ≈0.9375° per line (360/384) | The equal-division figure is a derivation, not stated in the sources — treated as unverified |
| 28 Lunar Mansions | 二十八宿 | KaiXi scale 365.25° vs. ShiXian scale 360° | Both scales coexist on real plates; whether the difference is precession or two different systems altogether is genuinely unresolved |
On a documented 36-ring San He plate, the principal rings run (from the center out): the heaven pool with its needle（天池）, the trigram and star rings, the inner 24-Mountain Correct Needle, the 24 solar terms, the 72 Dragons, the 120 Fenjin, the Human-plate Center Needle, a staggered fenjin ring, the 60 Dragons, the twelve qi and twelve field-allocation rings, the outer Heaven-plate Seam Needle with its own staggered fenjin and dragon rings, and finally the mansion-scale rings（宿度五行・周天宿度）.
Which layers the engine implements
The collation settles a scope question that matters for software: Xuan Kong needs almost nothing. Its irreducible set is the heaven pool plus one correct 24-Mountain Earth-plate ring plus the 360° circle (the 64-Hexagram ring only if one practices Xuan Kong Da Gua), and the star-assignment formula — because "one correct Earth-plate ring plus 360°" is all that sitting/facing, the lower-trigram/replacement decision (±4.5°/3°, see 24 Mountains & Degree Table) and the flying stars ever touch. The San He module is where the remaining rings live: the three needles, 72 Dragons and their five phases, 60 Dragons, the Correct-needle 120 Fenjin, the mansion scales, the Yellow-Spring and year-star harms, and the 360° scale. Implementing the narrow set is also the safer choice: fewer rings means a much smaller surface for the replacement/lower-trigram decision to go wrong.
Magnetic declination（磁偏角 cípiānjiǎo；繁體 磁偏角）and the compass
A magnetic needle points at magnetic north; the 24-Mountain table above is framed on true north. The difference between the two is the magnetic declination（磁偏角）, and the engine computes it itself rather than asking the user to supply a number — through an implementation of the World Magnetic Model WMM2025 in its compass module:
- Inputs and validity: declination is computed from latitude, longitude and elevation, valid for the model epoch range 2025.0–2030.0. Outside that window the engine refuses to extrapolate the model rather than silently returning a number the main field has drifted away from. Typical accuracy is about 0.5°–1° (1σ) at mid-to-low latitudes, degrading at high latitudes and in the South Atlantic Anomaly.
- Date semantics: the value needed is the declination on the day of the site survey, not the birth date — so the survey date is an explicit input (the engine never reads the system clock).
- The trap to avoid: declination and the Seam-Needle offset are unrelated quantities that happen to share a magnitude in one place and time. Shen Kuo recorded in the 11th century that the needle "always inclines slightly east"（常微偏東，不全南也）; today the declination across China is west-directed — about 7.53° west at Beijing for 2026.0 (Taipei went from +0.23° east in 1971 to −4.75° west in 2021). Anyone who "corrects" a reading by treating the 7.5° Seam Needle as a declination offset today adds the two same-signed errors together, pushing the result off by roughly 15° — a full mountain. The engine keeps the plate-ring selection and the declination correction as two separate switches, each declaring which north it refers to.
- How large declination actually is in China: the national range runs from about 0°21′ west (Lhasa) to 12°44′ west (Mohe), with no location anywhere near the model's blackout zone; the interpolation uncertainty at mid-latitudes is around 0.32° — far smaller than a phone magnetometer's own ±3°–5° sensor and environment error. Declination is real and must be applied, but it is not the dominant term in a handheld reading's error budget.
- The declination-free alternative: a solar compass（太陽羅盤）derives true north from the sun's position directly — the engine already computes solar positions for its calendar work — and sidesteps magnetic interference entirely; a calibrated sun-compass method reaches roughly 0.06° (1σ) against a phone magnetometer's ±3.8°–4.7° outdoors, which is the precision regime the narrow 3° replacement band demands.
Sources: collated against the repository rule tables (GB/T conventions for bearing notation and decimal degrees), the compass ring research notes, and the engine's WMM2025 compass module documentation. Where sources genuinely contradict each other (ring ordering, yin-house needle choice) the disagreement is disclosed above rather than averaged away; figures without a traceable source (specific ring counts beyond the documented ends) are omitted. No page-view or popularity claims are made anywhere on this site.