I'm doing engineering in the instance.

Chapter 17 Variables

The water pressure did not continue to rise.

They quickened their pace and walked about eighty meters. The pressure signal Xie Chengzhou felt under his feet slowly subsided, as if something upstream had shut off itself, not yet fully reopened. The water flow rate dropped from seven centimeters per second to five centimeters, and the water depth stabilized at twenty centimeters, no longer rising.

He mentally recorded the process: the pre-compression signal lasted for about three minutes, then faded away without triggering explicit rule one.

This is not a fluid anomaly; it is a harbinger.

He stopped, placed his hand on the pipe wall, and felt the current water pressure. Stable, normal, and basically consistent with the baseline data when they entered the pipe.

"Stop for a moment," he said.

Old Zhao stopped behind him, his breathing slightly rapid. He switched the thermos cup to one hand and held the pipe wall with the other.

Xie Chengzhou glanced back at Lao Zhao, said nothing, removed his hand from the wall, and wrote in his memo: "Pre-compression, first time, lasting approximately 3 minutes, spontaneously resolved, no fluid anomaly triggered. Water pressure returned to normal. Conclusion: Pre-compression is not equivalent to fluid anomaly; it is a precursor signal, and there is a possibility of a false alarm. Current location: approximately 250 meters."

He closed the memo and readjusted his pace to a normal walking speed.

Then he realized a problem.

In the "Site #002 Assessment Preparation" framework he established before entering the pipeline, the baseline walking speed for route planning was his own walking speed—about fifty meters per minute in an environment with a water depth of twenty centimeters. This figure was obtained by him through three tests while waiting in the first maintenance room: walking back and forth twice from the maintenance room door to the marked point on the pipeline wall, taking the average value, with an error within three percent.

He labeled it "Single-person speed" in the frame.

But now there are two of them.

He mentally estimated Lao Zhao's current pace: from entering the pipe until now, they had walked about 250 meters in about six minutes. That's about 41 meters per minute.

His own walking speed is 50 meters per minute, while Lao Zhao's walking speed is 41 meters per minute, a difference of about 18%.

The difference isn't significant on its own. But when he incorporates it into route planning, a problem arises: from the current location to the control room, there are still 550 meters to go. At Lao Zhao's speed, it would take about 13 and a half minutes, while at his own speed, it would take about 11 minutes. That's a difference of 2 and a half minutes.

Two and a half minutes is not a problem under normal circumstances.

However, the explicit rule states that after a fluid anomaly is triggered, the player must reach the nearest maintenance room within sixty seconds. The "maximum safe distance" he calculated within the frame—that is, the maximum allowable distance between the player and the nearest maintenance room when a fluid anomaly is triggered—is fifty meters. At a walking speed of fifty meters per minute, it would take about sixty seconds to run there, just inside the window.

But at Lao Zhao's pace, it would take him about 73 seconds to cover 50 meters.

It was thirteen seconds too long.

He wrote the number down in his memo and then drew a box next to it: "Safety distance correction: reduced from 50 meters to 34 meters (distance that can be reached within 60 seconds at Lao Zhao's walking speed of 41m/min). Route planning needs to be recalculated based on this: each segment of travel should not exceed 34 meters, and the location of the next maintenance room must be confirmed before proceeding."

This means his previous route planning is no longer valid.

"Old Zhao," he said, "how long did you walk through the pipes?"

Old Zhao switched the thermos cup in his hand. "During the construction period," he said, "this section of the pipe didn't have water yet. Every day we had to walk from one end to the other to do the inspection, which took about an hour and a half round trip." He paused for a moment, "After the water came on, we stopped walking that way."

"Does the water flow through these pipes?"

"Yes," Old Zhao said, "the old pipes in the city. Sometimes we have to go down to inspect them. The water is deeper and the flow is faster there." His tone was flat, as if he were talking about something familiar. "The fastest I've ever walked in the water is about 45 meters per minute, but that was on flat ground, without any debris, and with good lighting. Here—" He glanced at the pipe with his flashlight, "about 40 meters."

Xie Chengzhou noted this figure in his memo: "Old Zhao's maximum walking speed: 45 m/min (ideal conditions). Current conditions: approximately 41 m/min."

Then he recalculated the route plan.

From the current location to the second maintenance room, according to the copy rules, "the pipeline is 800 meters long and there are three maintenance rooms," the second maintenance room should be between 400 and 500 meters away. They are currently at 250 meters, approximately 150 to 250 meters from the second maintenance room. The error is too large.

He needs a more precise number.

"Do you know where the second maintenance room for this pipeline is?" he asked.

Old Zhao thought for a moment, "I'm in charge of construction acceptance, not design," he said. "But according to regulations, the distance between maintenance rooms for main sewage pipelines is generally no more than 300 meters. If the pipeline has bends or branches, the distance will be even shorter." He paused, "When you came in, I counted. The distance from the entrance to the first maintenance room is 120 meters. The second one should be 250 to 300 meters away, which is 400 to 450 meters away."

One hundred and twenty plus two hundred and fifty to three hundred equals three hundred and seventy to four hundred and twenty meters.

He compared this number with his own estimate: his estimate was 400 to 500 meters, while Lao Zhao's estimate was 370 to 420 meters, with the intersection being 400 to 420 meters.

他在备忘录里写：「第二检修室位置：约400-420米。当前位置：250米。剩余距离：150-170米。」

Then he replanned the route after adjusting the safety distance: each step should not exceed 34 meters, before proceeding, he should confirm that there are no sensors in the next section of the pipe, and after proceeding, he should stop to check the water pressure before moving on to the next section.

This is about 20 percent slower than his original plan.

He wrote the correction into the framework, and then added a line below it: "Speed ​​reduction: Acceptable. Safety boundary recalculation: Required."

He closed the memo and glanced at Old Zhao again.

Old Zhao stood beside him, holding a thermos in his hand, waiting for him to speak. He didn't rush him, didn't ask questions, he just waited. This was a way of waiting that Xie Chengzhou had seen on construction sites—the way experienced workers waited for project managers to make decisions. They knew that decisions took time, so they didn't disturb them; they waited to hear the results.

"I need to replan my route," Xie Chengzhou said. "It will take about three minutes."

"Okay," said Lao Zhao.

Xie Chengzhou propped the flashlight up on the pipe wall, letting the beam shine forward, freeing his hands to flip to the route map page in his memo and begin to replan.

He mentally divided the entire pipeline into several sections: from the current location to the second maintenance room, about 150 to 170 meters, divided into four to five sections, each 30 to 34 meters long; from the second maintenance room to the third maintenance room, the distance is unknown, and he will plan the route after reaching the second maintenance room; from the third maintenance room to the main control room, the same applies.

This planning approach is more conservative than the original "one-time planning throughout the entire process," but it is the only reasonable solution when information is incomplete. He used the same logic when conducting geological surveys in Bangladesh: when data is insufficient, do not make predictions beyond the scope of the data, keep the prediction boundaries within the range supported by the data, and then continuously revise them as new data is acquired.

He wrote down this logic in his memo: "Route planning principle (revised): Segmented planning, each segment not exceeding the upper limit of the safe distance, obtaining new information after reaching the new maintenance room, and then planning the next segment. Do not make long-term predictions beyond the scope of current information."

Then he closed the memo, took the flashlight off the wall, and said, "Let's go."

Old Zhao gripped his thermos tightly and followed.

They continued walking forward. Xie Chengzhou kept his pace at the same level as Lao Zhao's, neither too fast nor too slow. He would stop every thirty meters to feel the water pressure against the wall and only move on to the next section after confirming that the pressure was stable.

The pipes continued to extend ahead of them, black and deep, the sound of water echoing on the walls.

While walking, Xie Chengzhou mentally reviewed the number "Old Zhao's walking speed is 41 meters per minute" and then put it in the "known variables" column of the route framework, placing it alongside sensor locations, number of crawlers, and water pressure status.

Variables are not obstacles. They are parameters that need to be calculated.