The essential parts of the Samrat Yantra are the gnomon, a triangular wall with its hypotenuse parallel to earth’s axis, and a pair of quadrants on either side, lying parallel to the plane of the equator. On a clear day, as the sun passes from east to west, the shadow of the gnomon falls on the scale of the quadrant, indicating local time. You can see this illustrated in the time-lapse video below. Since a sundial gives the exact time for its particular locality only, a formula to obtain standard time is used that compensates for the longitude difference between the instrument location and its time zone, and the daily adjustment that must be made due to the earth’s orbit around the sun.