the origin of three points per acre: the emperor of the Ming dynasty set up the Xiannong altar in Beijing to worship Shennong. The Xiannongtan (also known as the "Mountain and River Altar"), located three kilometers southwest of Zhengyangmen in Beijing, has an observation platform inside, which is used as a place for the emperor to inspect the ministers' farming in spring. The farmland cultivated by the ministers in front of the observation platform (south) has one acre and three points. Later, "one acre and three points" was extended to "one's own small site".
At that time, the area of the land cultivated by the emperor was just the "one acre and three points" of the city system, so people extended it to personal interests or personal sphere of influence as "one acre and three points".