Tomb-Sweeping Day is a traditional festival. Why is it calculated according to the Gregorian calendar?

The lunar calendar in China is a combination of yin and yang. January is calculated according to a northern moon, and solar terms are calculated according to the position of the sun. The ancients swept the earth around the sun with an arc of 15 degrees, and established a solar term. Twenty-four solar terms are exactly 360 degrees, which is a circle. The highest day of the sun is defined as the summer solstice, the lowest day is defined as the east, and the days with equal days and nights are the vernal equinox and autumnal equinox, and the northern moon where the rain is located. Because the earth's orbit around the sun is about 365 days, and the interval between solar terms is about 15~ 16 days, there should be two solar terms in every lunar month. If there is a festival in any month, there will be one in the next month. Because solar terms are related to the sun, they are basically consistent with the solar calendar, but there is often a difference of one or two days, such as Qingming, sometimes April 5 and sometimes April 4. The lunar calendar and the Roman calendar overlap once in about 19. If you pay attention to the calendar, you will find that the solar terms are accurate to a certain time of a certain day. Therefore, the China lunar calendar is more advanced than the Roman calendar, and there is no error. The ancient people in China used armillary sphere and sundial compass to judge when the solar terms were, and used them to guide agricultural production, showing the intelligence and wisdom of the ancient people in China.