For time immemorial, shadows have been used to tell time with accuracy. This is the Jai Prakash Yantra, at the Jantar Mantar, Jaipur. Created under the supervision of Maharaja Sawai Jai Singh, this is the last of the instruments made at the observatory and said to be the most accurate of them all. The interesting structure is made of two interconnected cavities which are for each half of the year, depending on the hemisphere that the sun is on and spots details like hours, minutes, seconds and the zodiac signs to identify the month. The center of each instrument spots a iron ring that acts as an identifier for the earth’s equator.