Yantra Mandir
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The Yantra Mandir (commonly known as the Jantar Mantar) is an equinoctial dial, consisting a gigantic triangular gnomon with the hypotenuse parallel to the Earth's axis. On either side of the gnomon is a quadrant of a circle, parallel to the plane of the equator. The instrument is intended to measure the time of day, correct to half a second,[citation needed] and declination of the Sun and the other heavenly bodies.
Maharaja Jai Singh II of Jaipur constructed four Yantra Mandirs in Delhi, Jaipur, Ujjain and Varanasi. The most famous Yantra Mandirs are: