Vrihat samrat yantra the world's largest sundial which is in Jaipur Jantarmantar listed in UNESCO World Heritage Site..It works on sunlight and shadow mechanism to see the time in the past.
The Samrat Yantra, sometimes called “Supreme Instrument” is an equinoctial sundial of enormous proportion. Although one of the simpler instruments, and not too different from sundials which had been developed hundreds of years earlier, the Samrat Yantra is important because it measures time to a precision that had never before been achieved. The Samrat Yantra at Jaipur, for example, is capable of measuring time to an accuracy of two seconds.