Sundial - a device for determining the time to change the length of the shadow of the gnomon and its movement on the dial. The appearance of these hours due to the time when the people realize the relationship between the length and the position of the sun shade on those or other objects and the position of the sun in the sky.
The simplest sundial shows the true local, rather than the local mean solar time, and do not account for the difference between the official time and local solar time. Use the sundial can only during the day and in the presence of the sun. To improve the accuracy of a sundial to consider an amendment to the formula of time.
Currently sundial for its intended purpose are not used, and gave way to other various kinds of hours.