Sun clock algorithm

There is an error, which is the main reason for Runnian. It's simple.

This error is nearly 4 minutes a day, and a month is 120 minutes, which is nearly 2 hours. The annual difference (solar calendar) is nearly one day, so there is one more day in February, so the solar calendar year is only one more day in February, while the lunar year is 1 1-655. Just add one month to the next year to offset it, which is the lunar year, so it is one month. The rest of the time will continue to push back. By the way, it is determined that the lunar year is based on solar terms, with 2 solar terms per month and 24 solar terms per year. If it is short of a month, it will be replenished, so it is a month.