The sundial is one of the oldest and simplest time reckoning devices. It is based on the fact that shadow of an object changes with the position of the sun and hence time. Here we have a plate with a slit in it. The slit is aligned exactly in the geographic north – south direction and inclined at an angle equal to that of the latitude of the place. One can read the local time by the position of sunlight on the dial. In order to obtain the Indian Standard Time (IST), we have to add 19 minutes and 36 seconds to the local time.
Another correction from the graph known as 'Equation of Time' has to be applied to arrive at the precise time.

Sundial 1.jpg