Yantra
A yantra is a sacred geometric diagram that represents a deity or planet, drawn or engraved on metal, paper or wood. It is used as a focus for worship and mantra, and as a remedy for a planet.
Yantra means “instrument”. Some yantras are intricate designs, like the Shri Yantra of interlocking triangles. The planetary yantras are simpler: 3 × 3 number squares whose rows, columns and diagonals all add up to the same total, from 15 for the Sun to 39 for Ketu.
A Navagraha yantra brings all nine planets together for general balance, while a single planet’s yantra is used to support that planet. Traditionally a yantra is energised with its mantra (prana pratishtha) and kept clean in a place of worship, often facing east or north-east.
A yantra works through regular attention: lighting a lamp, chanting the planet’s mantra and keeping the practice steady. Simply owning one is not the point.
Choose a yantra for a planet that is helpful in your chart, and be wary of anyone who promises guaranteed results for a high price.