To lie in ambush means to enter the dog days.
"Summer solstice, three Geng's head falls", which is the basis for establishing the first fall.
The almanac stipulates: "Three Geng will count volts in the summer solstice". It means counting backwards from the summer solstice, and it will begin to subdue on the third Geng Day.
The "Geng Day" here refers to the day with the prefix "Geng" in the ancient "Ganzhi Jiri Law".
The date of Geng Day is changeable and not fixed, so the date of lodging is different every year, but the date of lodging is always between July 1 1 day and July 20.