Jantar Mantar in Jaipur is one of the 5 observatories that were built by Maharaja Jai Singh between 1727 to 1733. The original name of the stone observatory was Yantra Mantra but later due to incorrect articulation it became Jantar Mantar. This stone observatory has several instruments that help in calculating time and are useful also for studies related to celestial bodies. In the Rajput era it was a unique creation. One of the important yantras here is the Ram Yantra.

The Ram Yantra is instrumental in measuring the zenith distance and the altitude of the sun. The main feature of the instrument is that it gives the direct readings. As the tourists check out the instrument they will find that it comprises of two circular stone buildings. When seen together it becomes one unit. Though they are constructed at a distance they are complementary to each other. In the center of the two units there is a perpendicular rod is fixed. This particular rod is of the same height as the building.

Besides these there are twelve stone triangles that are fixed to the ground. These stone slabs are divided up from 90 degree to 45 degrees. The circular wall is marked off from 45 to 0 degree. It helps in calculating the movement of the stars.