Two Rings and a Centre
The inner ring is the 360 degree circle of Western astrology, divided into the twelve signs. This ring is used for calculation: it records exactly where the Sun, Moon, planets and lunar Nodes were at the moment being charted.
The outer ring carries the 64 hexagrams of the I Ching, laid around the wheel in a fixed order. This ring is used for interpretation. Each hexagram is one Gate, and each is divided into six Lines, giving 384 Line markers around the outer edge.
In the middle sits the BodyGraph. Because every hexagram on the outer ring corresponds to a Gate on the BodyGraph, a planetary position can be read straight off the wheel and marked on the figure.
How a Planet Becomes a Gate
Divide 360 degrees by 64 and each hexagram occupies just over five and a half degrees of the circle. Divide that by six and each Line occupies a little under one degree. When a planet sits inside a given segment at the moment of birth, the corresponding Gate and Line are activated. Human Design treats each of these segments as an imprinting field: a stretch of sky that colours the information a planet passes on. Finer subdivisions below the Line, called Colour, Tone and Base, give the wheel 69,120 distinct positions in total, which is why two people born minutes apart can still carry different charts.
Why Two Passes Round the Wheel
A chart is calculated twice: once for the moment of birth, which gives the Personality activations in black, and once for the moment roughly three months earlier when the Sun was 88 degrees back along the wheel, which gives the Design activations in red. Astrology only ever takes the first of these readings. The second calculation is what separates Human Design from its astrological root, and it is explained on the Personality and Design page.
The Wheel as a Synthesis
The Mandala is where the four root systems of Human Design visibly meet. Astrology and the I Ching are the two rings. The chakra system and the Kabbalah give the BodyGraph in the middle its Centers and Channels. Ra Uru Hu regarded the assembled wheel, rather than any single part of it, as the real discovery: one field in which the movement of the sky and the structure of the body can be read together.