"Pars Fortunae is a part of the astrological tool-kit that is amply explained in all elementary introductions in Astrology and everybody is aware that it is derived from the positions of the Sun, Moon and the Ascendant. But apart from that, all manuals maintain a stony silence about the logic, or the historical background behind it.

The Arabic parts (and Bonatti mentions about 100 of them) are in fact Egyptian in origin. They are numerological or arithmetical fictions and they have no physical basis, but are fictitious points on the ecliptic. 

First published on November 20, 2007, this author was the only Western astrologer using the tropical zodiac to correctly identify an Aquarian Ascendant for Barack Obama through medieval methods of natal chart rectification.  Two other successful efforts were made by astrologers using the sidereal zodiac.  As an update to the rectified time of 7:54:28 PM with an Ascendant of 27AQ09'12", this article provides out-of-sample tests which compare events of 2008 to dynamic measurements based on the 7:54:28 PM horoscope.  Despite an official birth certificate time of 7:24 PM rep

"Most astrologers have encountered the Part (or Lot as the Greeks called it) of Fortune, but have little idea of what to do with it. The modern literature on the subject is of little help tending to make it an extremely abstract symbol, something "karmic." To complicate things further, it is now clear that for approximately 50% of all people the Part of Fortune is usually computed incorrectly, namely those persons born at night between sunset and sunrise. I'll come back to that in a moment.

"The term 'Arabian Parts' is misleading. The medieval Arab astrologers inherited their art from a long-established tradition, which they did much to refine and develop, but did not originate. References to the parts are found in all the major astrological texts that have survived from Greek and Roman times. One such account is given in the Mathesis of Firmicus Maternus, written in the 4th century.

" In astrology, the Part of Fortune, sometimes called Fortuna, is the most popular Arabic Part. Arabic Parts are sensitive points in a chart, and are calculated using specific formulas whereby two planets or points are added together, and a third planet or point is subtracted from that result."