Everyone left in a flash, and Elder Niu, who was forced to stay, mooed and said:

"Just chat as if I, Old Cow, don't exist."

After what they did, even Master Zhao felt a little embarrassed.

Not to mention the little bamboo, which looks like a blushing peach blossom.

In fact, they had a lot of contact over the past few months. But as the saying goes, the eldest competed with the second, but defeated the third. Because Li Mingyue and Jiang Xueying fought against each other secretly and guarded against each other, Xiao Zhuzi had no chance to take advantage of.

As a result, the two of them became even more estranged from each other than when they were in the capital.

The silence became more and more awkward as time went by. Young Master Zhao coughed lightly and said with a smile, "I only know a little bit, I'll just tell you a little bit, Uncle Niu can correct me if I'm wrong."

But Elder Niu ignored him and just drove his boat. Old Niu wished he could find a crack in the ground to crawl into.

"Okay." Zhang Xiaojing nodded, and listened to Zhao Hao explain to her how this big ship used the rudder to steer, the compass to check direction, the hourglass to tell time, and the starboard to position.

Xiao Zhuzi became distracted while listening, thinking that it had been a long time since he last listened to Mr. Zhao's class.

She suddenly thought that after returning to Beijing, she could continue to listen to Mr. Zhao's science lectures at home, which seemed like a good idea.

Thinking of this, she couldn't help but feel a little excited, and she was no longer so resistant to returning to Beijing.

~~

"That's it." Young Master Zhao pointed to the compass map on the table with one hand and the compass needle with the other and said, "We can enter the Black Water Ocean after five o'clock with the Danyin needle... Uh, Xiaojing, did I not explain something clearly?"

"Ah?" Xiao Zhuzi came back to her senses and waved her hands with a red face, saying, "No, no, Mr. Zhao explained it very well."

She quickly calmed down and asked, "What does the fifth watch mean?"

Elder Niu's hand slipped and he almost pushed the rudder out.

"..." Mr. Zhao couldn't help feeling ashamed, thinking that all his talk about feelings was in vain.

"Is it the same as our fifth watch at night?" Zhang Xiaojing asked embarrassedly, racking her brains.

"The length is the same. A day is divided into ten equal parts." Zhao Hao nodded and pointed at the hourglass fixed on the dock. "When this hourglass runs out, it's one update."

He paused, and continued, "However, 'geng' is also a unit of speed on the ship. One geng is about 60 miles. If it is slower than this speed, it is called 'but no geng'. If it is faster than this speed, it is called 'over geng'."

"Then how do we know how fast the ship is and whether it has changed shifts?" Zhang Xiaojing was now completely interested and asked hurriedly.

"This one." Zhao Hao turned around and looked at Elder Niu and said, "Show it to Miss Zhang."

"Moo..." Elder Niu tried not to speak and used his eyes to signal his apprentice who was helping him operate the pole.

The disciple picked up a book-sized wooden board and ran to the bow of the boat.

Through the porthole, Zhang Xiaojing saw him exert a slight force and throw the wooden board into the sea.

With a snap, the board landed flush with the bow.

The young apprentice quickly ran towards the stern. Zhang Xiaojing saw that each of his steps was of the same distance and his pace was also very fixed, just like the wound-up soldier dolls made by Master Zhao, which was quite funny.

"This is the result of hard work." Zhao Hao explained, "Every time you run from the bow to the stern, the time must be the same, otherwise you won't get any food."

"Can this measure speed?" Zhang Xiaojing asked puzzledly.

Zhao Hao pointed to the wooden board floating on the sea and smiled without saying anything.

Zhang Xiaojing saw that the wooden board had almost moved to the stern of the boat without her noticing.

She was a good student who could get 100 points on the test. She immediately started thinking and in a blink of an eye, she clapped her hands and said crisply:

"I understand. After the board enters the water, it can be considered stationary for a short period of time, but the boat keeps moving forward, so it will soon be thrown to the stern. If people start running at the same time and reach the stern at the same time, then it can be considered that the speed of the boat is the same as the speed of the people running. Therefore, people need to be trained to run from the bow to the stern, in order to improve the accuracy of the measurement."

"Hahaha, not bad." Zhao Hao gave a thumbs up and said to Elder Niu, "How about it, isn't my female disciple very smart?"

"Moo..." Elder Niu thought to himself, it turns out to be a female disciple. Then the old cow shouldn't be here anymore.

"But sir, what if it's cloudy and rainy and the deck is difficult to navigate?" Zhang Xiaojing finally got into the mood. "And what if we need to measure speed at night and can't see the water surface clearly?"

Elder Niu's expression froze. He seldom sailed at night, and had never thought about this problem. He thought to himself, "It's okay if it happens."

"If you want to be able to sail all-weather, it's actually very simple." Young Master Zhao smiled, as if nothing in the world could stump him. "Tie a long rope to a wooden board and throw it over the stern. Then it only takes a short time to calculate the speed of the boat from the length of the rope."

"And this method is more convenient and accurate!" Zhang Xiaojing's eyes lit up and she said excitedly, "As long as we do the calculations in advance and mark the rope, even an illiterate sailor can report the speed right away."

Now it was Mr. Zhao's turn to be ashamed. Girl, you must be so smart. I just nodded and you answered quickly...

As expected of an idol's daughter, my idol has good genes!

Elder Niu's eyes also lit up. Although he didn't understand 'distance divided by time equals speed', he intuitively felt that this method was the same as the principle of measuring speed with a wooden board. If it was really as the two said, it could be used all-weather, more accurate, and could be operated by illiterate people, then it would be a great improvement.

"That's right. As long as we tie knots at equal distances on the rope, we can easily measure the speed." Zhao Hao said to Elder Niu with a smile, "I asked someone to make a few ropes like this before I came. Let's give it a try?"

"Yeah." Although Elder Niu didn't dare to say anything, he was very tempted. However, the caution of a sailor made him dare not believe anything easily.

~~

So Elder Niu handed the rudder to his apprentice, and followed Zhao Hao and the other two to the stern of the ship.

Xiwa also brought things over. In addition to the speed measuring rope that Mr. Zhao mentioned, there was also a round timer.

This device is an improved "hourglass speed measurement method" by European sailors based on the "wooden board speed measurement method" of the Ming Dynasty. They used ropes with equal distances to measure distance and a 14 or 28 second hourglass to measure time. In this way, the speed of the ship can be expressed by observing the number of knots released every 14 or 28 seconds.

To this day, the unit of ship speed is still called "knot"... However, the fact that one knot is equal to about 1,852 meters is just an artificial regulation, so Mr. Zhao defined one knot as one thousand meters from the perspective of unified measurement.

In other words, in his territory, there is no concept of sea miles.

At the same time, in order to round off, he also changed the time unit to 18 seconds. In this way, the distance between the two knots changed from the inhumane British 23 feet 7.5 inches to a refreshing 5 meters.

Zhao Hao also improved the hourglass into a clockwork timer. As long as the lid of the round timer is screwed to the end, a clockwork sound will be heard inside, and the lid will turn back. After 18 seconds, there will be a clang, the timer ends, and the rotation stops.

The structure of this thing was even simpler than the mechanical doll he gave to Zhang Xiaojing. For Zhao Shizhen, who had dismantled several Western clocks, it was a piece of cake.

Of course, Zhao Shizhen dismantled clocks in order to make guns, and the clockwork timer was just an insignificant by-product.

ps. Fourth update, please give me your monthly vote!