Mo Ke arrived early to Qinbei Hospital on the day of his therapy. Some people liked to be early hoping to get seen early, but he went specifically to attend Li Yun’s morning class. He wasn’t a medical practitioner, but he was interested to learn about Li Yun’s approach to medicine, especially after Li Yun’s announcement that he was interested in proving the existence of meridians. Mo Ke’s grandfather had taught him gua sha, a technique of using a smooth surface to scrape the skin. It was the main reason why he wanted to participate in Li Yun’s project to find a cure for Usher’s Syndrome.

From the hallway, the door of the classroom was opened. Mo Ke peeked inside and realized that he should have arrived earlier. The room was packed, which was unusual since only the registered students were allowed. The majority of the people in the room weren’t residents, but the attending doctors.

“Today, we will talk about age,” Li Yun announced to the room. “What are the techniques a mortician uses to identify a person with no IDs?”

“Their teeth,” a resident from the orthodontic department answered. “Teeth are more closely correlated with growth and development than bones. Using eruption, mineralization, and other methods can identify the age within a year of accuracy.”

“But only for adolescents, how about adults?” Li Yun asked.

“How about radiocarbon dating of the bones?” asked Wei Bing.

“A bit more accurate, but without destroying the bone itself?”

“DNA analysis like the Horvath clock?” Asked another resident. “Scientists can identify age within three years of accuracy based on the Horvath clock, a method of analyzing the DNA methylation.”

“Three years is still a big range. Anything else?” Li Yun asked.

Everyone thought about their previous lesson. Li Yun was teaching them about the power of observation. Even the most scientific method to estimate age had flaws and limitations, so they wondered how accurate face readers were.

“How accurately can a face reader estimate age?” asked the students.

“Pretty accurate,” Li Yun said, but the residents looked skeptical. Even the best facial recognition software couldn’t determine a person's age.

“How so?” Fan Gang asked.

“Before I get there, I have a question. As doctors, what purpose do we have when we ask about a person’s age?” Li Yun posed. “We know it’s important to identify a growing child from a mature adult and an aging senior. We associate all of this with age because we can easily mark it in association with time, a relatively constant construct based on the Earth rotation around itself and the sun. So constant that our body has a biological clock based on it.

Birthdate also gives us a marker in time for us to compare. Let’s look at Dr. Fan for example, he’s twenty-three based on his birth record, but his mental and biological age is eighteen, what does this mean?”

“He’s still a child?” Wei Bing joked.

Li Yun smirked. “Maybe, but which age is more accurate?”

The residents thought the birth record was more accurate.

“It’s relative,” An Luchang responded. “Mental age is subjective based on overall intelligence and performance of the mind, biological age is based on our body's overall function.”

“So a twenty years old man with a sixty years old mental age, does that make him a time traveler?”

The residents scratched their heads and discussed it amongst themselves. “Doesn’t a time traveler have knowledge of their past?”

“Ah, I see, then the time traveler must have memories of past events in order to be a time traveler?” Li Yun asked. “What if a piece of memory was sent back in time, and a person receives it, is it still considered time travel?”

“Could be…” The residents were confused, wondering when the class had turned into a physics class.

“Well, we are straying a bit off topic, but everyone at least understands that age can be a fluid concept,” said Li Yun. “So if a face reader like me tells a person like Fan Geng that they are eighteen, am I technically also right?”

“It’s still b******,” Fan Geng had heard about plenty of scammers before, but Li Yun was really stretching some logic, which was the trademark of scammers.

“While that’s also true, it’s very important as doctors to think outside the box when dealing with medical cases,” said Li Yun. “The key to our previous lessons have been about observation and being the observer. And once we obtain enough data from our perspective, it is also important to see everything from another perspective to gauge the true nature of an illness.”

Li Yun drew on the computer screen a triangle, “I am sure you understand the basic concept of triangulation. The patient's history and physical condition are the basis for diagnosing an illness. We often use biopsy and various exams to confirm the diagnosis. But what if you're dealing with a patient who has no history and doesn't want to give you their information? You need other methods to fill in those missing data.”

The students nodded as Li Yun continued on with his lesson. After the class, Mo Ke met with Li Yun, who gave him a bottle of pills. Li Yun nicknamed the pill Yintang as the meridian channel in the region was most active when he injected the medicine into his veins.

Li Yun returned home and documented his findings about Mo Ke in his journal. After writing in the journal, Li Yun meditated and entered his memory palace. There were many discoveries about the dantian and his system that he needed to store, but he didn’t want to have physical evidence of them before he understood what they met...

For months, he had been collecting information on people’s dantian in his memory library. After collecting over thousands of data sets, he began categorizing and grouping all the dantians from the people and patients he had met. One of the most interesting aspects of the data he had extrapolated from the data was age.

Of the three main corners of the pyramid, jing qi shen, jing fluctuated the most during a person's lifetime. The dark yin jing was acquired through the parents. Babies born from healthy parents had an average of 70 max yin jing, but the side of the pyramid was very dim, indicating that the yin jing was still weak, around 20. It typically took two to three years for the newborn to recover the yin jing energy. Babies from parents with poor lifestyles had as low as twelve max yin jing, and they often experienced many complications. However, Li Yun had patients in their 80s and 90s with low yin jing, so age wasn’t entirely affected by the yin jing.

Yang jing was something affected by the lifestyle. It wasn’t developed fully until the body matured, between thirteen and twenty-one. The range varied greatly from 10 to 90. Active and healthy individuals had higher max yang jing, while inactive ones had lower. Li Yun often considered the yang jing as the energy level of an individual, which could be restored to maximum after consumption of food, sleep, and sex. The problem was, an excess of any will cause the yang jing to reduce. Even worse, addiction and laziness reduced the overall max jing of both the yin and yang.

Qi was the energy that traversed between the dantian and physical realm. It was the driving force behind the meridians and the unexplained phenomenon that happened inside of Li Yun’s body. The yin and yang Qi was typically the same amount within 2 points and rarely ever used up. A baby was typically born with 74/74 yin and 74/74 yang Qi, Li Yun could use up his Qi during Zuowang, Qivi, and Spirit Detection, but it seemed that only practitioners had the ability to utilize Qi.

Li Yun could sense Qi in people and some artifacts, but wondered if there were Qi around them. In theory, Qi existed everywhere, but couldn’t be detected. Li Yun wondered if it had to do with movement. The Qi in everyone’s body was in constant random motion, along with the energy inside the artifacts. However, objects without an activated Qi couldn’t be detected because it wasn’t in motion? Zhuangzi once said that wind was the Qi of Earth, so it was likely that the motion of qi was the key to Li Yun being able to detect it.

Yang Shen was strongly associated with accumulated charm, spirit, and mental resilience. Everyone's maximum shen was very similar but varied in intensity. Yang Shen was 1 at conception, around 60 at birth and max out in the thirties around 90.

The yin Shen, in contrast, was full at birth, from 90 to 100. It neither increased or decreased. The only exceptions were practitioners, who seemed to be capable of using up yin shen energy. When Li Yun met Shang Cang, his yin Shen level was around 80/100, but his yang Shen was 23/88.

It took Li Yun a while to understand the nature of the fourth corner that appeared to be fixed. There was a high possibility it represented the physical body. Li Yun had originally scaled the physical body to 100 like the system, but having met a couple of centurions, Li Yun had decided to scale it up to 150. It was by using this method that Li Yun was able to see the correlation between age. The fourth corner grew more intense and opaque with every rotation around the sun.

In comparison to others, Li Yun’s dantian technically had 140 yin jing, 170 yang jing, 190 yin and yang qi, 190 yin and 200 yang shen. The scaling the system had used was more of a percentage than a direct numbering system. The more information he gathered, the more he realized how shallow his understanding was of meridian. Maybe the true perfection of meridian was realizing that it doesn’t truly exist, how ironic would it be?

Li Yun’s phone suddenly went off at around midnight. He peeked at the messaging app, everyone was wishing him a happy birthday and asking him to go out with them on the weekend. Li Yun looked at the date, May 24th… Was it already his birthday? From behind, Rouxi warmly hugged him and bit his earlobe. One didn't need to be a fortune teller to know what happened afterward.