Out of the ten poruthams prescribed by South Indian Astrological rules this comes first and is also called as "Nakshatras Porutham".
Hindu Rashi/ Nakshatra Matching
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In South India, Nakshatra Matching is done to check the Jathagam Porutham of the bride and groom. It is mostly done when the marriages are arranged by the families of the boy and the girl.
Why it is important - Dina Porutham
The first and the foremost of the ten poruthams is the Dina Porutham; it is also referred to as Dina Koota. The availability of dina porutham in the charting denotes good health and prosperity for both the husband and the wife with freedom from poverty, sicknesses and disease; the two are therefore expected to enjoy all comforts in a long and a happy married life. For this reason, dina porutham is considered vital for a marriage,
But whatever the case may be,the 27th nakshatra, that is the last star has to be rejected from any calculation.