The basic concept of Nadi Astrology is “Nadi” (nāḍi). There are 150 Nādis in a sign or Rāshi (Rāsi); one sign is 30 degrees of the zodiac 360. Twelve signs of zodiac are grouped into three categories: Movable (Chara), Fixed (Sthira) and Dual (Dvisvabhāva) signs. The nomenclature of 150 Nādis is peculiar to each of these three types of signs. There are 1,800 Nādis in 360 degrees. Numbers and names of Nādis are identical among all four Chara signs. Among all four Sthira signs, numbers and names of Nādis are identical, but numbering is different from those in Chara and Dvisvabhāva signs. Similarly, numbering of Nādis in all four Dvisvabhāva signs are identical among themselves, but different from Chara or Sthira signs. For instance, the first Nādi in Chara signs such as Aries is Vasudhā Nādi, but in Sthira signs the order is reversed and Vasudhā is 150th Nādi. In Dvisvabhāva signs such as Gemini, Vasudhā is 76th Nādi; that is, from the middle of 150. Thus, there are 450 distinctive names and numbers in the full zodiac. Nādi texts use this concept of Nādi as the basic unit for prediction. That is why they are called “Nādi amshas”.
Chandra Kalā Nadi, which is also known as Deva Keralam, was published by Sagar Publications in 1992, edited and translated into English by R Santhanam. It is a compilation of over 82 hundred verses by Achyut of Kerala, that is why it is called “Deva Keralam”. But its original kernel was Chandra Kalā Nādi, which has not been preserved as a separate text. Deva Keralam has borrowed many non-Nādi concepts also in order to make the book fuller, but it preserves the gist of Nādi astrology. However, there are many different trends in Nādi Astrology which are not present in Deva Keralam. There are Nādi texts named after planets, such as Guru Nādi or Shukra Nādi, and there are voluminous unpublished texts like Dhruva Nādi. The palm leaves in Tamil Nādu temples use a style different from that of Deva Keralam, and the Tamil method of Nādi Astrology is paralleled by Bhrigu Samhitā in North India, which has been published in part, but many spurious publications in the name of Bhrigu Samhitā have also appeared in the market.
The basic methodology of these Nādi or Samhitā texts have never been described in these texts, hence astrologers can predict only what they already possess, and are dumb-founded when they do not possess the required leaf about some particular person. The most fundamental trait of Nādi texts is Nādi, which is actually a sum total of all divisions of a sign caused by sixteen divisional charts (shodasha vargas) described in texts like BPHS (Brihat Parāshara Horā Shāstra). 135 divisions out of total 285 are repeated in other divisionals; hence there are exactly 150 distinctive divisions of a sign. But these divisions are unequal; largest division being of half a degree, and the smallest division is 36th part of a degree. Another school of thought assumes that all 150 divisions are equal; the value being 12 minutes (arc) in length.
When predictions are based on Nādis in which ascendant and planets are placed; it means the combined results of all sixteen divisional charts are being told. Hence, Nādi Astrology is the most detailed and accurate method. But it requires highly precise birth time, and it also requires knowledge of genuine Nādi texts, most of which are unpublished, and the custodians do not allow others to see the manuscripts. The same is the case with Samhitā texts in North India, such as Bhrigu Samhitā or Rāvana Samhitā
ravati or Hyderabad.”