That old almanac book knows that it is in the first place.

From midsummer to the third Geng day in the future, it began to rise and fall. One volt refers to the day before the third Geng day from summer to the fourth Geng day in the future. Erfu (Midfu) usually refers to the day before the fourth Geng Day from summer to the first Geng Day after beginning of autumn. Three volts (terminal volts) refers to the period from the first Geng Day after beginning of autumn to the day before the second Geng Day (ten days in total).

The dog days refer to the first, middle and last three days, which appear between the summer heat and the summer heat, and are the days with the highest temperature and the heaviest humidity in a year. It is very hot every year after entering the dog days, especially during the dog days. There is a folk saying that "Sanjiu is cold and Sanjiu is hot".

The annual stay time is not fixed, and the length of stay is also different, from mid-July to mid-August. Lodging time needs to be calculated by consulting the yearbook. Lodging date can be simply expressed by the formula of "from summer to the third night in the future", that is, from summer to the third night in the future, the initial lodging is 10 day, the intermediate lodging is 10 day or 20 days, and the final lodging is 10 day.