Why do calendars have advantages and disadvantages? Where do all the statements in the calendar come from?

Calendar originated from the yellow calendar, which is a kind of almanac that can display various calendars such as solar calendar, lunar calendar and dry calendar at the same time, and has a lot of rules and contents related to seeking good fortune and avoiding evil. In ancient times, the almanac was calculated and published by Qin, so it was also called the almanac. Its content guides the farming opportunities of Han working farmers, so it is also called the farmers' calendar. Han people are commonly known as general books.