Pullen SD (Neo-Porphyry)The house system Pullen Sinusoidal Delta (also known as Neo-Porphyry house system) determines the house sizes from a sinus function depending on the size of the quadrants. You can find more detailed information on the mathematical process in the Documentation of the Swiss Ephemeris, chapter 6.1.5.3. One peculiarity of this house system is the fact that when a quadrant is smaller than 30°, the middle house of the quadrant takes the size 0. The house system was invented in 1994 by the American astrologer Walter Pullen (born 1971), the author of the astrology software Astrolog.
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