The Jantar Mantar was built to measure the local time, the Sun's declination, altitude, the declination of stars, planets and to determine eclipses The Jantar Mantar at Varanasi has several masonry instruments to record the motion, speed and properties starts and planets and study astronomy that are accurate and can still be used efficiently today. The Jantar Mantar incorporates multiple structures of unique form, each with a specialized function for astronomical measurement.
These structures with their striking combinations of geometric forms have captivated the attention of architects, artists, and art historians. Originally, there were many yantras (instruments). Some of the important ones are the Krantivritta Yantra, Digansha Yantra, Samrat Yantra, Prakash Yantra, Ram Yantra, Disha Yantra and Dhruva Yantra.