Nadivalaya Yantra, is a version of an equinoctial sun dial quite different from the design of the Samrat Yantra. The two circular plates that are facing the north and south and are parallel to the axis of the rotation of Earth. The movement of the shadow of these rods indicates the time. Jantar Mantar at Jaipur, built by Maharaja Sawai Jai Singh II, is one of the largest stone observatories in the world.