A bodygraph is astronomy plus a fixed table: where 13 celestial bodies stood at birth and about three months before it, and which gates and lines those positions fall into. Below is exactly what we calculate, with what data, and control dates anyone can check in any other service.
The positions of the Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto come from astronomy-engine (Don Cross, open source). It is built on the VSOP87 planetary theory and a lunar model and is accurate to within one arcminute. For scale: one Human Design line is 56′15″ wide, so the error is dozens of times smaller than a line.
Positions are geocentric, corrected for aberration, in the tropical zodiac (measured from the vernal equinox). Earth is the point opposite the Sun (+180°). The difference between terrestrial and universal time (ΔT) is applied by the library automatically.
The lunar nodes are true nodes: the osculating node, the point where the plane of the Moon's actual orbit at that moment crosses the ecliptic. We compute it from the Moon's position and velocity in the same ephemerides — as Swiss Ephemeris and most Human Design services do. The South Node is opposite the North Node. In late October 2026 we replaced an approximate node formula (a few of Jean Meeus's correction terms, off by up to 17′) with this exact calculation: in some charts a node's line and the Environment and Perspective arrows changed, and in about one chart in 125 a channel did too.
The unconscious (red) side of the chart is not taken “88 days before birth” but at the moment the Sun stood exactly 88° of ecliptic longitude earlier than at birth. Because Earth's orbital speed varies, that is roughly 86 to 92 days. We find the moment by iteration until the Sun's longitude matches the target far more closely than a line, then calculate all 13 bodies at that minute.
The zodiac circle is divided into 64 gates of 5°37′30″ in the order of the Rave mandala. The first, gate 25, begins at 28°15′ Pisces (358°15′ longitude). Each gate has 6 lines of 56′15″, then colors, tones and bases, from which the variables are derived. Type, authority, profile, definition and incarnation cross follow from these activations by fixed rules: a channel is defined when both its gates are active, a center when it lies on a defined channel.
Charts most often disagree between services not because of astronomy but because of an hour: a person is born on local time, while planets are calculated in universal time (UTC). So we never guess the offset from longitude or from today's rules.
A limitation worth knowing: for births before 1970 the IANA database has gaps in some regions. If you were born earlier and in a small town, compare the UTC offset the chart shows with a reference such as the astro.com atlas.
The birth time. The Moon crosses a line in under two hours and a gate in about half a day, so an error of even 15–30 minutes can change the Moon's line, sometimes its gate, a channel or the type. The Sun changes line about once a day, so the profile only changes when the Sun was near a line boundary. More in the Basics section.
Between services there can be rare one-line differences in the lunar node gates: some use the true node, others the mean one. We use the true node. The Variables (color and tone) are so fine that even a fraction of an arcminute between ephemerides sometimes changes the base.
The calculation engine is covered by automated tests: the gate and line of every activation are checked against the wheel formula from the open hdkit project on 80 charts, hdkit's reference chart matches to within an arcminute, and the gate → center table is checked independently. Below are control dates chosen to test the trickiest part — historical time zones. The result is calculated live by the same code as your chart.
Soviet time: until 1990 Kyiv kept Moscow time — UTC+3 in winter, not today's UTC+2.
Moscow summer time — UTC+4. A service applying today's rule would be an hour off.
An ordinary modern case: Kyiv summer time, UTC+3.
The energy crisis: in January 1974 the US went on year-round daylight time — UTC−4 instead of UTC−5.
The British Standard Time experiment of 1968–1971: Britain stayed on UTC+1 through the winter.
A half-hour zone — UTC+5:30.
Southern hemisphere, daylight time UTC+11: in universal time the birth is still on 30 December.
Enter any of the control dates on our chart page and in another service — Jovian Archive or MyBodyGraph, for example — and compare the type, profile, authority and the Sun's gates and lines. If you find a difference, write to us: we look into every case.