Jiang Si had been learning painting from her master since she was a child, so she recognized at a glance that the handwriting on the outside of the envelope was from her master's hand.

And she also knew that the master wrote with his left hand.

But she was surprised that her master suddenly wrote to her and sent her things.

Jiang Si was quite surprised.

Although the master's wife did not tell her where the master had gone, Jiang Si could roughly guess it from her words.

The master must have been seconded to a ton security unit.

This can be seen from the mailing address which is a mailbox.

Thinking of this, Jiang Si quickly opened the envelope and read it at a glance.

"What did the letter say?" Huo Tingzhou saw her serious expression and suddenly had a bad premonition in his heart.

Thinking of the last time that Master Fang's wife was assassinated by spies, he couldn't help but frown.

"Is Professor Yu okay?"

"It's okay, it's not what you think."

Jiang Si took a deep breath and tried to keep her voice steady. "See for yourself."

Huo Tingzhou took the letter and quickly flipped through it.

The content of the letter is very brief.

No greetings, no explanations.

It said: [The parts in the package must be drawn with the highest accuracy in three views (front, top, and side views), a plan view, and detailed cross-sectional views of key parts.]

[During the drawing process, dimension lines need to be marked, no specific values are required, ratio: 1:1. ]

【After completion, please seal and send back to this mailbox.】

If they didn't both know Professor Yu's way of doing things, they might have thought it was a prank.

While Huo Tingzhou was reading the letter, Jiang Siyi had already opened the package sent by her master.

One of the packs is all drawing tools.

Jiang Si took a quick look and thought that these things should be specially customized and could not be bought on the market.

In addition, there is a metal part wrapped in thick velvet next to it.

It is the size of a palm, and the shape looks somewhat complicated, covered with fine grooves and interfaces.

"This should be a part of the rocket engine."

Huo Tingzhou had some knowledge in this area. He took it and looked at it carefully for a while.

"This is connected to a centrifugal pump, but it is a model that has been eliminated overseas."

"Eliminated?"

Although Jiang Si was surprised, she always felt that this matter was not that simple.

It would take at least a month to complete such a precise drawing.

The master wouldn't be so idle as to send her a discarded part.

Could it be that the master was deliberately testing her level?

Huo Tingzhou thought so too. After pondering for a moment, he suddenly had a bold guess in his mind.

"This time they sent an obsolete model, maybe next time it won't be..."

Jiang Si: "You mean it's under development?"

"That's right." Huo Tingzhou nodded.

If he guessed correctly, the development of rocket engines might be nearing completion.

During the production process of these fine parts, all drawings have to be drawn by hand to prevent leakage.

After that, it will be manufactured by different military factories.

Finally, these parts will be transported to the Beijing Aerospace Base, where they will be assembled uniformly.

What Jiang Si has to do is to draw the complex three-dimensional mechanical structure into a one-dimensional drawing with an error as low as millimeter level.

Otherwise, during the rocket launch, there is a possibility that the launch will fail due to this tiny flaw.

After listening to Huo Tingzhou's analysis, Jiang Si was silent for a moment.

She walked back and forth in the living room several times, and asked after a long time.

"Do you feel anything strange?"