Sawai Jai Sîngh II decided to build astronomical observatories. Starting in 1724, the first observatory was completed in Delhi, the place where the controversy began regarding planetary positions. Thus, India began to appreciate for the first time instruments of masonry and massive stone. The Maharajah astronomer continued to carry out experiments and observations for nearly seven years, during the time that the observatories were constructed. Thereafter, he reformed the imperial calendar and established the value of ecliptic obliqueness as 23° 28 '.

With these creations, Sawai Jai Singh II made studying astronomy and astrology easier. His observatories were used as laboratories, where one could test oneself on various calculations and check them by practical observations. Formerly, these observatories were used to accommodate academic seminars, conferences, discussions, and, especially, to prepare ephemeris tables, calendars and almanacs.

The small equatorial sundial (Laghu Samrat Yantra), can measure time to a precision of about 20 seconds. Twin armillary sphere instruments (Jai Prakash Yantra) use small ring suspended on wires over each marble bowl. During the day, the shadow cast by the ring can be used for determining the solar position. At night, one peered up through the ring from beneath the marble slabs of the bowls to determine star positions. The two bowls are complementary- where one has slabs, the other has slots. The bowls were used alternately from one hour to the next.