Jantar Mantar was built by the founder of Jaipur, Jai Singh II, during the period of 1728 to 1734. Jai Singh II had a passion for astronomy and scientific inventions. He was not satisfied with contemporary metal astrolabes. He worked out a way of making permanent structures to measure time, the position of the stars and planets. Jantar Mantar reflects the ideals of Jai Singh II. He built four other observatories in Varanasi, Ujjain, Mathura, and one for the imperial city of Delhi. The observatory, Jantar Mantar, was the essence of the city of Jaipur. It was a novel idea that was in many ways ahead of its time.
Each instrument employed in this observatory serves a particular function and each gives an accurate reading. Small Samrat is a large sundial with flanking quadrants marked off in hours and minutes. Dhruva locates the position of the pole star at night and those of the 12 zodiac signs. Small kranti is used to measure the longitude and latitude of celestial bodies.