How is the calendar made, such as how accurate the judgment of solar terms is?

Calculation, different calendars have different calculation methods.

In ancient China, because agricultural production strongly depended on farming time, it was an important function of the government to publish the calendar.

The specific calculation method is mainly the calculation of the length of one year and the dates of various landmarks, and then the specific date of each solar term is determined according to various formulas.

For example, at the vernal equinox, the astronomical definition is that the sun moves to 0 degrees of the Yellow Meridian and 30 degrees of Grain Rain.