Davison Relationship Chart (Average Relationship Chart)
Davison Relationship Chart: construction principle, interpretation, spherical mean method (Kutalev correction), and option settings in the Zeus astroprocessor.
1. Overview
The Davison Relationship Chart is one of the methods of relationship analysis that allows constructing a single chart for a couple or group of people. The method was developed and described by the British astrologer Ronald C. Davison in his book “Synastry” (1977).
Unlike the Composite Chart, which is built on the basis of the average planetary positions in the zodiac, the Davison Relationship Chart is a real chart: it is calculated for a specific moment in time and a specific geographical location, computed as the averages of the corresponding data of two (or more) partners.
Construction Principle
To construct the Davison Relationship Chart, the following are calculated:
- Average birth time — the arithmetic mean of the birth dates and times of the partners. The dates are converted into a continuous time series (Julian days), the average value is found, which is then converted back into a calendar date and time.
- Average place of birth — the arithmetic mean of the geographical latitudes and longitudes of the partners’ birthplaces.
The resulting date, time, and place serve as the input data for calculating an ordinary “root” chart. This is what makes the Davison Relationship Chart unique: unlike the composite chart, it exists “in reality” — for example, directions, progressions, and transits can be fully applied to it, just as with any ordinary chart (radix).
Interpretation
The Davison Relationship Chart describes the quality and nature of the union as such — not the personalities of each partner separately, but that “third entity” which arises in the space between them. The planets in the chart show the dynamics and resources of the relationship, the Ascendant and houses — the form in which these relationships manifest in life, and the aspects — the internal tensions and harmonies of the union.
The method is used for the analysis of romantic and marital couples, as well as business partnerships, friendships, and family relationships. When data on three or more people is available, the chart can be calculated for the entire group — the averaging principle is preserved.
2. Spherical Mean (Kutalev Correction)
The Problem with the Standard Method
When constructing the Davison Relationship Chart, the standard method for calculating the birthplace of the relationship chart uses the simple arithmetic mean of geographical coordinates: latitudes are added and divided by two, longitudes — likewise. This is exactly how Ronald Davison himself described the calculation.
However, this approach has a significant flaw: it implicitly assumes that the Earth’s surface is flat (or more precisely — cylindrical), whereas in reality it is a sphere. On a sphere, the geometrically midpoint between two coordinates does not coincide with the point calculated through the arithmetic mean.
Illustrative Example
Take two points: 60° N, 0° E and 60° N, 180° E. The arithmetic mean gives a result of 60° N, 90° E (or W, depending on the program). But the actual midpoint between them on the surface of the globe is the North Pole (90° N). The discrepancy is 30 degrees of latitude.
The general pattern is as follows: the farther apart two places are in longitude and the farther they are from the equator, the farther north (or south) the real midpoint compared to the result of a simple arithmetic calculation.
When This Matters
For most couples whose birthplaces are within the same region — such as British couples in Davison’s own examples — the discrepancy between the two methods is negligible and has virtually no effect on the chart. It is not surprising that Davison himself did not attach importance to this: the scale of the British Isles is too small for the error to be noticeable.
However, in the case of couples from geographically distant regions — for example, from Russia and Korea, from Europe and South America, from Scandinavia and Japan — the difference in the calculated coordinates can be quite significant and lead to a noticeable shift in the house cusps, up to the Ascendant moving into a different sign.
Practical example. A couple where one partner was born in Moscow and the other in Seoul: the difference in the results of the two methods is so significant that the houses in the chart shift noticeably, which directly affects the interpretation.
Authorship of the Method
This method of geodetically correct calculation of the midpoint on a sphere was proposed and introduced into astrological practice by Denis Kutalev, who raised this issue on astrological forums and on his own initiative achieved the implementation of the corresponding algorithm in a number of astrological programs. By right of priority, this approach may be called the “Kutalev correction”.
💡 Recommendation: when working with couples whose birthplaces are significantly distant from each other in longitude — especially at high latitudes — it is recommended to use the calculation based on the spherical mean to obtain geometrically accurate coordinates for the Davison Relationship Chart location.
3. Calculating the Davison Relationship Chart in the Zeus Astroprocessor
The Davison Relationship Chart can be calculated in the Zeus astroprocessor from two places: from the Event Pool and the Database. You need to select at least 2 events (radixes), then select Davison Relationship Chart from the context menu. The calculated chart will appear at the very bottom of the current event list.
Both methods of calculating geographical coordinates for the Davison Relationship Chart are supported, giving the user the ability to choose between standard arithmetic averaging and the geodetically correct spherical mean. When the spherical mean option is enabled (currently for two selected events only), the program calculates the average geographical point taking into account the spherical shape of the Earth — that is, it finds the point on the surface of the globe equidistant from both (or all) birthplaces along the great circle arc. The result may differ noticeably from the standard arithmetic one, especially when birthplaces are widely spread in longitude and at high latitudes.
When the option is disabled, the program uses the standard Davison method — the simple arithmetic mean of the coordinates — which ensures compatibility with the results of most other astrological programs.
Usage Recommendations
| Situation | Recommended Method |
|---|---|
| Both partners from nearby regions | Standard (arithmetic mean) |
| Partners from different continents or distant countries | Spherical mean |
| High latitudes + large spread in longitude | Spherical mean |
| Comparison with other programs | Standard (for compatibility) |