What is a sundial? Where is the largest sundial in the world?

 A sundial is basically a simple clock, where a stick is fixed on a flat surface. The surface is marked such that the shadow of the stick shows the time. The world’s largest Sundial is in Jaipur and is called the Samrat Yantra, or “Supreme Instrument”. The Samrat Yantra is an 89-foot-high and 148-foot wide-sundial. When the sun moves across the sky, it casts a shadow on the finely calibrated arms extending on either side of this sundial. It measures local time, zenith distances, meridian pass times, and the declination of the stars.