How to distinguish seasons with standard tables

The method of identifying seasons with standard tables is as follows:

The standard watch is an astronomical instrument in ancient China that used the length of the sun shadow to judge the seasonal changes. It consists of two parts: the standard watch and the watch.

The ancients called poles or pillars standing upright on the flat ground "watches". The sun shines on the watch and casts a shadow. It was found that the shadow of the watch was always cast in the true north direction at noon, so a ruler made of slate was laid flat on the ground, perpendicular to the vertical watch. One end of the ruler is connected to the watch base, and the other end extends to the true north direction. This ruler made of slate is called "Gui".

Later, people found that noon was the shortest day in the hottest time of the year, so this day was designated as the summer solstice. Later, it was found that in the coldest time of the year, one day had the longest sun shadow at noon, so this day was designated as the winter solstice.

In ancient times, the "watch" was eight feet high, almost as high as the eyes of a person of medium height. On the summer solstice, the shadow cast by the eight-foot-high "watch" is exactly one and a half feet, so the size of "Gui" is set at one and a half feet. In ancient times, people took the summer solstice as the beginning of the year. Every time the shadow cast by the "watch" is one and a half feet, the new year begins.

Therefore, the ancients in China have long known that a year is equal to more than 365 days. Later, the ancients changed the winter solstice to the beginning of a year, so they changed the size of "Gui" to one foot three feet, because the shadow cast by an eight-foot-high "watch" on the winter solstice was exactly one foot three feet.

The watch seems simple, but it is actually very useful. It can not only measure the winter solstice and summer solstice, make a calendar and calculate the 24 solar terms, but also determine the orientation and even measure the land. When surveying a large area of land, the distance can be calculated according to the standard shadow length at the same time and in different places.

Generally speaking, if the shadow lengths of standard meters differ by one inch, then the two standard meters are separated by 1000 mile. It can be seen that this standard has played a considerable role in primitive society.