The gnomon casts a broad shadow; the shadow of the style shows the time.
The gnomon may be a rod, wire, or elaborately decorated metal casting.
Lastly, to adjust for daylight saving time, the sundial must shift the time away from solar time by some amount, usually an hour.
This correction may be made in the adjustment plaque, or by numbering the hour-lines with two sets of numbers. The hour lines are spaced equally about the circle, and the shadow of the gnomon (a thin cylindrical rod) rotates uniformly.
The style must be parallel to the axis of the Earth's rotation for the sundial to be accurate throughout the year.
The style's angle from horizontal is equal to the sundial's geographical latitude.
The sundial's indicated solar time thus varies from clock time by small amounts that change throughout the year.
This correction — which may be as great as 15 minutes — is described by the equation of time.
This correction is often made by rotating the hour-lines by an angle equal to the difference in longitudes.As the Sun appears to move across the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of day.The style is the time-telling edge of the gnomon, though a single point or nodus may be used.A spot of light may be formed by allowing the sun's rays to pass through a small hole or by reflecting them from a small circular mirror.Sundials also may use many types of surfaces to receive the light or shadow.