Tianjin is in the middle and late July every year. According to the historical meteorological records of official website, "declination" refers to when the longitude of the sun reaches 120 degrees. In Tianjin area, according to historical meteorological data and statistical results, the dive time is from mid-July to late July every year. Entering volts means entering "three volts". There is a folk saying that "the three gengzi heads fall on the summer solstice", which is the basis for establishing the first autumn. The almanac stipulates that "the number of volts starts from the third day of the summer solstice", that is to say, "the countdown starts from the summer solstice" and begins to fall on the third "Geng Day".