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South Indian Panchagas traditionally follow Vakya Panchanga System or Drik Ganita Panchanga System. Drik Ganitha Panchanga is based on the positions of the planets calculated with more accurate astronomical algorithms. Sayana (Western – Tropical) longitudes are calculated and Nirayana (Indian – Sidereal) positions are arrived after deducting a yearly constant called Ayanamsa. Even Prof. Krishnamurthi suggested Drik Ganitha for horoscopes.
Vakya panchanga is based on vakyas (sentences / formulae / mnemonics ) to arrive at the positions of the planets. For example “Viththera Naathana” sentence may mean a Moon ascension of 0° 12′ 3″.
Suitable corrections shall be applied on a periodic basis called bija sanskar. The last correction was done centuries ago. But Krishnamurthy Paddhati followers and others suggest that for Nita Anushthanas daily chores you can follow simple Vakya calculations and other rigorous mathematical should be used for Predictive Astrology.
So Vakya is needed for daily practices and festivals and functions at local temples. More importantly Vakya system is followed in Nadi Astrology inscriptions and the same has evoked recent interest and lot of books have come out on the topic.
Secondly accuracy of planetary position is not the factor in predictive Astrology. The positions only give a clue to the Astrologer whose psyche, intuition etc and these mental subconscious faculties of Astrologers are more important per se in predictions. For the same combination, different astrologers and seers see different results which are contradictory completely. Great Astrologers with high precision computers fail to predict correctly most of the events, whereas some of the street sooth sayers come out with stunning predictions with aplomb.
You can generate panchangams based on these ayanamsas free online at Raja Panchangam http://rajapanchangam.com