In Tamil Nadu, the texts are mainly written in Vattezhuthu which is an ancient Thamizh (Tamil) script. They were written by an ancient priest or "Rishi" called Agasthiya who had a highly developed consciousness. These ancient records of providence were made famous by practitioners around the Vaitheeswarankoil temple in the state of Tamil Nadu. First, the Naadi palm leaves are located based on the thumb impressions (right for men, left for women).
These Naadi leaves were initially stored in the premises of Thanjavur's Saraswathi Mahal Library in Tamil Nadu. The British colonialists later showed interest in the Naadi leaves concerned with herbs and medicine, future prediction, etc. Some leaves got destroyed, and the remaining were auctioned during the British Raj (rule). These Nadi leaves were obtained by the families of astrologers at the Vaitheeswaran Temple and have been passed down the years from one generation to the other.
There is also another set of astrologers claiming that the content written in the palm leaf is a conversation between Shiva and Parvathi. This is called "Shiva Nadi Jyotisiyam".
The basic methodology of these Nādi or Samhitā texts has 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 But it requires highly precise birth time, and it also requires knowledge of genuine Nādi texts, most of which are unpublished, and the custodians do not allow others to see the manuscripts.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.
All beings, irrespective of species, nationality, religion, social class, aggressiveness, etc., are controlled by the Navagrahas (nine houses or planets). The Navagrahas are very sincere in their duties as cosmic public servants and never deviate in performing their duties. They cannot be bribed. They affect individual beings as well as entire societies as per the Karma (thoughts, words, and deeds of beings in this world as well as other worlds) applicable. The current life path of a person is determined by past Karma. For example, if a person is blessed with wealth in this birth, then it implies this person has done many punyas (activities that resulted in good Karma) in his/her previous births and he/she is enjoying the benefits of it in this birth. It is like a person who has saved a lot of punyas in his or her account cashing it in when the need arrives.
Birth, death, rebirth and moksha are all controlled by our karma. Paapams (activities that result in negative Karma) are obstacles that may take long to dilute whereas punyas earned can be 'spent' very soon. From the Hindu point of view, this makes it important that we always think good thoughts and do no harm to any other being. Bad Karma is committed even if we think unrighteous thoughts.
What is to be given to your lot in life, when, how, and where are all decided by the Brahma using the Navagarahas and the Siddars as channels. As the Brahma cannot do everything in our realm directly, 84,000 Siddars have been created to perform duties on its behalf. Siddars are only another level of public servants in the cosmos, and they have capabilities and energies many would consider supernatural, although in Hinduism this is quite normal. Of all the siddars, 84,000 are identified as very powerful and these siddars express themselves by way of Naadi. Agathiyar is the leader of all Siddars - Agathiyar along with Kakapujandar, Bokar. Agathiyar always thrived for Jeeva Karunyam (to not harm any being), i.e., taking care of all living things in this world and guiding them to the path of Gnana or the attaining of supreme self-knowledge.
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