Just as there are nine houses in Astrology, on the same basis is specially prepared the navgraha yantra. This yantra is particularly beneficial if some couse is casting an adverse effect on you or if there is lack of peace in your house or if your house has not been subjected to Navgraha shanti ritual.
In this center navgrah yantra is constructed in two ways :-
Navaratna mudrika- A nine stone sing (mudrika) is also constructed and made available to the sadhaks this mudrika is made from pure silver and gold and it is subjected to pran pratishtha before it is given. There are separate tantras for the nine grahas.
If you propose or wish to worship a particular graha then again a separate yantras are available for all the none grahas. There tantras are subjected to pran pratishtha as per the mahoorat or auspicious time. They are (1) Surya tanra (2) Chandra yantra (3) Guru Yantras (6) Shukra Yantra (7) Shani Yantra (8) Rahu Yantra (9) Ketu Yantra