Why two degrees changes your whole chart
Published 2026-08-20
Eight Mansions (八宅, Ba Zhai) divides the compass into eight palaces of 45° each, which puts their edges at 22.5°, 67.5°, 112.5° and so on around the circle. A building measured at 22° and the same building measured at 24° therefore land in different palaces, and the two answers are not neighbors in any useful sense.
At 22° the front faces North, the house sits South, and it is a Li house (離宅), East group. At 24° the front faces Northeast, the house sits Southwest, and it is a Kun house (坤宅), West group. Two degrees of measurement error, and every sector in the chart changes sides.
The same eight sectors, read from both bearings
| Sector | Li house, from 22° | Kun house, from 24° |
|---|---|---|
| North | Yan Nian, favored | Jue Ming, weak |
| Northeast | Huo Hai, weak | Sheng Chi, favored |
| East | Sheng Chi, favored | Huo Hai, weak |
| Southeast | Tian Yi, favored | Wu Gui, weak |
| South | Fu Wei, favored | Liu Sha, weak |
| Southwest | Liu Sha, weak | Fu Wei, favored |
| West | Wu Gui, weak | Tian Yi, favored |
| Northwest | Jue Ming, weak | Yan Nian, favored |
The four sectors one reading calls favored are the four the other calls weak, so every downstream answer moves with them: which corner takes the bedroom, which corner takes the bathroom, which corner you were told to leave to storage.
That happens because these two houses are in opposite groups.
Only half the boundaries do this
The eight edges are not equally dangerous. Taking a bearing one degree either side of each edge:
| Edge | One degree below | One degree above | Group changes |
|---|---|---|---|
| 22.5° | Li house, East | Kun house, West | yes |
| 67.5° | Kun house, West | Dui house, West | no |
| 112.5° | Dui house, West | Qian house, West | no |
| 157.5° | Qian house, West | Kan house, East | yes |
| 202.5° | Kan house, East | Gen house, West | yes |
| 247.5° | Gen house, West | Zhen house, East | yes |
| 292.5° | Zhen house, East | Xun house, East | no |
| 337.5° | Xun house, East | Li house, East | no |
Four of the eight edges flip the group. The other four move you to a different house inside the same group, and there the damage is much smaller than it looks. Crossing 67.5° takes a Kun house to a Dui house, and both treat northeast, southwest, west and northwest as their four favored sectors. Not one sector changes from favored to weak. What changes is which of the four star names sits on each of them — the sector called Sheng Chi in the Kun chart is called Yan Nian in the Dui chart.
So a bearing near 67.5° that turns out to be two degrees off costs you the star labels and leaves the room-by-room verdict standing. A bearing near 22.5° that is two degrees off costs you everything.
Away from an edge, two degrees costs nothing
The reverse is also true, and it is the part that usually goes unsaid. A house measured at 180° sits 22.5° from the nearest edge — the furthest from one you can get. At 178°, 180° and 182° it is a Kan house every time, and so it would be anywhere from 158° to 202°.
Add up the zone where a two-degree error can move you: three degrees either side of eight edges is 48 of the 360 degrees, about 13 percent of the bearings you could measure. Most bearings sit safely in the middle of a palace. The problem is that you cannot tell which case you are in until you have looked at the number.
What the tool does about it
The compass bagua map checks the distance from your bearing to the nearest palace edge and warns you when it is three degrees or less. Enter 23° and the report says so in as many words:
23° is 0.5° from the boundary between two palaces. A re-measurement two degrees the other way would change the house chart and every line in this report. Take the bearing again before acting on any of it.
Without that line, a chart built on 23° looks exactly as confident as one built on 180°.
Three degrees is our threshold, not anybody’s tradition. It is set there because phone compasses indoors are often off by several degrees, so a reading closer than that to a line is not a reading you can build on. Widen the threshold and the warning fires on bearings that are fine; narrow it and it stays quiet on bearings that are not.
What the warning cannot do
It cannot tell you that your bearing is wrong. Nothing in the code knows what direction your building actually faces — it knows the number you typed, and whether that number is close to a line. If you measured 24° and the true facing is 21°, the tool will warn you that you are near an edge and then build a Kun house chart, because 24° is a Kun house.
Getting off the edge is a measurement problem, not a software one: how to take a compass bearing indoors covers the part you have to do yourself. And none of this says that a favored sector produces a result you can measure. Eight Mansions names sectors, this site reports what it names, and method and assumptions sets out where that stops.