The primary use of a sundial is to tell time based on the position of the sun. A sundial consists of a flat plate or surface, usually marked with hours, and a gnomon, which is a vertical stick or triangular blade that casts a shadow on the surface. As the sun moves across the sky, the shadow of the gnomon shifts, indicating the time on the marked surface. Sundials were one of the earliest time-measuring instruments and are still appreciated today for their simplicity and elegance. They are often used in gardens and parks, serving both a functional and decorative purpose.