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A [[Predictive Method|predictive method]] based on the Earth's axial
rotation. Roughly every 4 minute period after birth - which is the the time
needed for the Medium Coeli to progress by 1 degree (1 degree right ascension
of the Medium Coeli; [[RAMC]]) - is equivalent to one year in a person's
life. This method is only used to progress the [[Axis|axes]], with other
methods being used for the planets such as [[Secondary Progression|secondary
progressions]] whereby each day after the birth is equivalent to one year.

The method of primary directions can only be used with birth times accurate
to within a minute, because otherwise the inaccuracies in prediction are
simply too large: A birth time inaccurate by one minute would lead to any
prediction being incorrect by one year.

==Interpretation==

The following points are considered to be significant:

* An axis which forms an aspect to a factor in the [[Natal Chart|natal chart]] is regarded as a [[trigger]], which means that it activates the factor in question.

* When an axis changes signs by progression it signals a change of theme.

==Supplemental Information==

The above information from the encyclopedia deviates a bit from modern practice in primary directions.  The following text reflects a fuller consideration of the elements that go into the practice of primaries.  Rumen Kolev has written two small booklets called "Primary Directions I & II" which give a modern and clearly written presentation of primaries (there is a bit of math in the presentation, but this is unavoidable if you want to get a good understanding of the subject).

The main idea of primary directions is to move radix points on the celestial sphere in the direction of their daily motion in ascension (some people also use converse directions, moving them in the opposite direction). Effective use of primaries depends on a precise radix time. But this is also the reason that primaries are a powerful rectification tool. 

Aspects of directed points to radix points (planets, cusps, sometimes even abstract points such as the PoF) are considered meaningful, as are reflections of radix and directed points around the main axes (local meridian and horizon).

There are variations in method along several dimensions: 

# Domification method. All systems of primary directions are associated with a quadrant house system that is capable of yielding "mundane" positions or "house longitudes". Historically, Regiomontanus, Topocentric and Placidus have been most used, though other well-defined systems such as Campanus can be used. Placidus is the most common method and its model of ascension is the most accurate.
# The kind of points to direct (promissors) and to which to direct (significators). The choice is between bodies with latitude ("mundo directions") or between ecliptic intersects of points ("zodiacal directions"). The latter is the more traditional method, while most modern astrologers who use primaries use the former. 
# The key used. This is the mapping of motion of the RAMC to time. There are two kinds of keys: static and dynamic. Static keys use an uniform rate of motion (degree for a day, Naibod, Cardan, etc). Dynamic keys vary the mapping based on astronomical motions (the Kepler key, equation of progressed sun in longitude to RAMC). 
# Uniform movement of all points or use of a time equivalence that includes actual planetary motion. Traditionally, all points are moved uniformly with their directed positions being calculated on the basis of advancement of the RAMC, but ignoring any proper motion due to the passage of time. This uniform motion is the common understanding of the word "direction".  Another view is to consider the direction to be a mapping of an earlier time in the native's life to a transit time. In this approach, sometimes called "primary progressions", the proper motion of the planets between the radix and directed times is taken into account by erecting a normal chart for the directed time and comparing its mundane positions to those of the radix.

When using software to calculate primary directions, it is important to understand how the program decides among the above alternatives, and what options it offers to select among them.
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