He was betrayed at the beginning, from a cake seller to a wealthy person

The forceps were ready but the prince would not be back for a long time, so Lu Yan had some free time. She had promised to give Lu Sheng a complete plan and there was no reason to regret it.

She really needed to come up with a serious plan. Since she had already acknowledged her relationship with Lu Sheng, it would be a bit inappropriate to continue avoiding it.

To be honest, the contraceptive methods in ancient China were very poor, which was why Lu Yan was reluctant to take action.

One of the major methods of contraception in ancient China was drugs. There is a recipe for frying mercury in oil in Qianjin Fang. Put the mercury in a pot and fry it for a day. After it cools down, eat a jujube-sized one. Then you will never get pregnant. Lu Yan actually believes that this method can be used for permanent contraception, but it is hard to say whether she will survive.

There is a recipe in the Jiayou Materia Medica: take one foot of old silkworm paper and mix it with wine. This method is not poisonous, but it doesn't seem to be very useful.

Most of the records about contraceptive recipes in ancient times are useless. If they were really useful, there wouldn’t be so many cases of infanticide and abandonment.

Some Western countries have records of using fish bladders and sheep intestines as condoms, but they are obviously not very useful because if the size is not right, there is really nothing to say.

After much thought, the only way is to calculate the date + peripherals. Some ancient people didn't even know that menstruation was related to fertility, let alone calculating the date.

Normal women of childbearing age have menstruation every 28 days on average. The period from the beginning of this menstruation to the first day of the next menstruation is called a cycle. Each cycle of women can be divided into menstrual period, ovulation period and safe period. Stopping sexual intercourse during the ovulation period is a contraceptive method of ovulation period contraception.

女性的排卵日一般在下次癸水前的14天左右，在排卵日前3~4天和排卵日后5~7天内容易怀孕，属于危险期。其他时间则较为安全。

To be on the safe side, you can determine a 5-day period for the days of menstruation, which is a relatively safe range. In this way, you can calculate the dangerous period lasting 16 days, plus the 7-day menstrual period, so there are only about 7 days in a month that are relatively safe.

Lu Yan calculated the time and laughed at herself. Seeing him writing and drawing on paper, Lu Sheng was very curious and came over to ask Lu Yan what she was calculating. Lu Yan told him how to calculate the safe period, and Lu Sheng was stunned.

Lu Sheng repeated: "You mean you won't get pregnant these days?"

Lu Yan shook her head: "It's just a little less likely. The only way to be completely safe is to not do it."

Lu Sheng automatically ignored this sentence, picked up the paper excitedly and read it again and again, and said excitedly: "You are so amazing! You can even calculate this!"

Lu Yan looked at Lu Sheng with amusement: "I thought you would regret that there are only seven safe days in a month."

"It's already pretty good." Lu Sheng said, "Does this mean that these days we can...?"

Lu Yan laughed and said, "You wish. You still have classes to go to. Don't even think about it before you finish your apprenticeship!"

"What class?" Lu Sheng leaned in closer and asked, "When does it start?"

"I can't explain it to you." Lu Yan said, "Go find some classic books on this subject, as well as some fire avoidance diagrams and the like, and bring them to me so I can explain it to you."

Fire avoidance maps are usually prepared by parents for their newly married daughters, and are put in their dowry as a gift. Lu Sheng and Lu Yan were not planning to hold a wedding, so the old couple naturally would not prepare this for them, so they had to make it themselves.

Ever since Lu Yan issued this order, Lu Sheng would think about these things every day when he was on duty or not at work.

Classic books were easy to find. The Su Nu Jing was a famous classic in this area, and he could find it if he wanted to. But the fire avoidance map was difficult to get. There were no decent bookstores in Liaozhou, and he had already looked everywhere. He could only ask his brothers who were married.

The first thing he had to do was to find his father. He really couldn't open his mouth to his own father.

Lu Sheng turned around and looked at Nie Li who was flipping through the account books beside him, thinking. He knew that Nie Li was married, and he brought his wife over from his hometown after settling down here. But they had no children, so he never asked about it.

Nie Li felt his gaze and raised his head to look at him: "Master Lu, have you been looking at me?"

Lu Sheng leaned in closer and whispered, "Let me ask you something...Have you ever bought a fire avoidance map yourself?"

Nie Li looked up in surprise and raised his eyebrows: "You and your wife want to use it?"

Lu Sheng nodded slightly: "I've looked in all the bookstores here, but it's not there. I don't know where to get it."

Nie Li was a little confused: "Where is the book you got when you got married? Why are you suddenly looking for this one again?"

"It's hard to explain in a few words." Lu Sheng sighed: "You just need to know that I'm in urgent need now."

"We don't sell it in Liaozhou. If you want it, I can give you the one I have at home." Nie Li said, "My copy is at the bottom of the box anyway. If you want to use it, I'll find it for you."

Lu Sheng nodded in surprise: "It has to be you, Brother Nie! Then bring it to me tomorrow, thank you for your help."

Nie Li nodded in agreement.

Lu Sheng solved his most pressing problem and could continue working with peace of mind.

Nie Li was arrested as soon as he returned home.

Madam Nie stood at the door and looked at Nie Li rummaging through the boxes with a puzzled look on her face: "What are you looking for?"

Nie Li was startled and patted his chest: "Madam, you scared me!"

Madam Nie walked in: "What are you looking for?"

Nie Li shook the old fire avoidance map he took out and said, "It's useful."

Madam Nie narrowed her eyes: "What's the use?"

"That can't be told to you." Nie Li said as he walked around Madam Nie and left the bedroom.