Chapter 108: The Third Floor of the Lab Building

Monday, 6:20 a.m. Dawn had not fully broken yet. Blue-gray mist drifted along the edge of the athletic field, and a thin layer of frost clung to the blades of grass. Lin Chen opened his eyes on the dormitory's hard board bed, and the first thing he did was reach for his left foot. The bandage had already yellowed, and along its edges seeped the faint smell of iodine, mixed with the sourness of sweat. He sat up and slowly moved his foot to the side of the bed. When it touched the floor, it felt as though he were stepping onto a thick sponge soaked through with water—there was no pain, only a heavy sinking sensation. He drew a deep breath, braced his ankle with his right hand, and used that leverage to stand upright. His knee trembled slightly. He waited three seconds, made sure his center of gravity would hold, and only then let go.

He washed up and splashed cold water on his face. From the iron box under the bed he fished out the last half of a compressed biscuit and swallowed it with the cooled boiled water in his enamel mug. Crumbs caught in his throat; he forced them down, his Adam's apple bobbing. The ledger was under his pillow. He opened it and looked at the cash column: negative 1.9 yuan. Beside it he added a new line: Monday 06:40. Lab building. Transport: on foot. Cost: weight-bearing on foot. Remaining margin: none.

At 6:40 sharp, he appeared in the lobby on the first floor of the lab building. The voice-activated light in the stairwell was broken; only the green glow of the emergency exit sign remained, casting the place in dim light. Holding the handrail, he made his way up one step at a time. His left foot could not bend, so he had to climb with that leg kept straight. Each time he lifted his knee, the muscles in his thigh tightened until they shook. He counted the stairs: one, two, three... By the time he reached the third floor, a layer of cold sweat had already broken out across his back. The door to Room 302 stood slightly ajar. Pale fluorescent light spilled from inside, and he could hear the faint rustle of turning paper.

He knocked. His knuckles struck the wooden door softly. From inside came a low voice: "Come in."

Teacher Zhou sat behind an old wooden desk by the window. Several yellowing competition papers lay spread across it beside an old oscilloscope. He looked around fifty, with graying hair, wearing a washed-out synthetic shirt with the sleeves rolled to his forearms, exposing the veins standing out on the backs of his hands. He did not look up, only pointed at the chair opposite him. "Sit. What happened to your foot?"

"An old injury." Lin Chen sat down and set his canvas bag by his feet. The strap was frayed at the edges; he had wrapped it with transparent tape.

Only then did Teacher Zhou raise his eyes. His gaze rested on Lin Chen's left foot for two seconds, but he asked nothing more. "Chen Hao said you wanted to know the route into the internal extra assessment. I have one blank exceptional recommendation form here. But I don't sign blank checks." He pulled an A4 sheet from the drawer and pushed it across the desk. "Three questions on it. A mechanics derivation in physics, transient circuit analysis, and one logic-gate design problem. You have forty minutes. Solve them, and I sign. Fail, and you go back and prepare for the first mock exam like everyone else."

Lin Chen took the sheet. The questions were not beyond the syllabus, but the angles of attack were unusually tricky. The first required deriving the corrected formula for the period of a simple pendulum in a non-inertial frame. The second concerned the response curve of an RC circuit under a step signal. The third asked for a self-latching alarm circuit built entirely with NAND gates. There were no hints, no standard answer format. Only blank space.

He pulled out his fountain pen and unscrewed the cap. The instant the nib touched paper, a sharp stab of pain shot through his left foot, as if a needle were driving upward along the nerve. He clenched his back teeth and slowed his breathing. Don't panic, he told himself. Break it down. Known conditions: gravitational acceleration g, pendulum length L, non-inertial-frame acceleration a. Hidden condition: equivalent gravitational field. Scoring points: vector composition, small-angle approximation.

He began sketching on the scratch paper. Force analysis, rotated coordinates, the expression for equivalent gravitational acceleration g'. His pen moved fast, but his handwriting remained neat. Second question: the differential equation for capacitor charging. He remembered that Chapter 3 of Foundations of Electronic Information Experiments had mentioned Laplace transforms, but he had never studied them systematically. So he switched to the time constant τ=RC, wrote the voltage-change formulas piece by piece, and drew an exponentially rising curve. Third question: truth table, Karnaugh-map simplification, logic-gate connections. He drew with extreme care, labeling every pin with a number, even marking the jumper symbols at every crossing in the wiring diagram with perfect clarity.

Forty minutes. The second hand of the wall clock ticked on. Teacher Zhou said nothing. He merely watched the oscilloscope screen and from time to time jotted a few notes in his notebook. In the laboratory there was only the scratch of pen on paper and the sound of Lin Chen's restrained breathing.

Lin Chen set down his pen. The back of his hand was slick with sweat, and his knuckles had gone faintly white from gripping too hard. He pushed the paper across.

Teacher Zhou picked it up and read it from beginning to end. His gaze paused on the graph in the second problem. "You didn't use Laplace?"

"I don't know it," Lin Chen said evenly. "I approximated it with the time constant and a piecewise function. Error stays within five percent. Good enough for an exam room."

Teacher Zhou did not comment on whether it was right or wrong. He only asked, "If the equipment has poor contact during the exam and the waveform on the oscilloscope is jittering, how do you tell whether the problem is the signal source or the probe grounding?"

"Disconnect the probe first and check the noise floor. Then switch channels and compare. Finally, check the impedance on the ground lead." Lin Chen answered quickly. He had worked out that sequence while learning capacitor replacement from the repair-shop owner. It wasn't in the textbook, but it existed in the real world.

Teacher Zhou nodded. He drew a red pen from the holder and marked three circles on the paper. "First problem: you reversed the direction of the equivalent gravity vector. Minus two points. Second problem: your approach is correct, but the mathematical tool is too clumsy. In the exam room, you won't have enough time. Third problem: the logic is correct, but you didn't account for fan-out. In a real circuit, it would burn out." He pushed the paper back. "But you can break an unfamiliar problem into known modules within forty minutes, and you know the lower limit of acceptable error in an exam setting. That's more useful than a standard answer."

He opened the drawer, took out the exceptional recommendation form, signed his name in the field labeled "Supervising Teacher's Opinion," and stamped it with his personal seal. "Take the form. But don't get happy too soon." Teacher Zhou looked at him. "The internal extra assessment doesn't test rote memorization. It tests live troubleshooting and code debugging. On Wednesday's first mock exam, if you fall out of the top sixty in the grade, this sheet becomes waste paper. The school administration looks only at scores, not process."

"Understood." Lin Chen accepted the form. The paper was thin, but the ink of the seal had not yet dried, and when he touched it, a dark red smear stained his fingertip.

"And one more thing." Teacher Zhou took a brass key from beneath the desk and set it on top. "Fourth floor, east side, Room 407—the abandoned electronics lab. Every afternoon after school until six, the door will be open. There's an old signal generator inside and a scrapped multimeter. You can use them. But before Friday, work out the Laplace-method solution for the second problem and write it on the blackboard. If you can't, the key comes back to me."

Lin Chen picked up the key. The edge of the metal was cold, carrying the smell of machine oil and dust.

"Thank you, Teacher Zhou."

"Don't thank me." Teacher Zhou lowered his head over the papers again. "You walk your own road. A foot injury isn't an excuse—it's a variable. Calculate your margin properly."

Lin Chen walked out of the lab building. By then the sunlight had pierced the mist and fallen over the concrete of the athletic field, steaming up a thin veil of vapor. He went slowly down the stairs. Every step was still heavy, but his breathing stayed steady. He tucked the recommendation form into his ledger, together with the deferred-exam application and the medical certificate. One more link had been cut from the chain of tolerances.

When he got back to the classroom, the morning self-study bell had not yet rung. More than half the students were already there, the sounds of page-turning and recitation blending together. He opened his notebook of corrected mistakes and, on the blank space of the physics-experiment page, wrote: Variable: internal extra assessment. Status: recommendation secured. Conditions: first mock ≥ top 60 / Laplace solution completed before Friday.

He lifted his head and looked at the blackboard. Another day had dropped from the countdown placard. There were two days left until the first mock exam. Four days until the Provincial Institute of Science and Engineering verification.

In the front row, Chen Hao turned around and handed him a folded slip of paper. "Teacher Zhou sent you over there? He's got a strange temper, but his eye is viciously sharp. I managed to get a photocopy of part of the practical-question bank for the internal extra assessment. It's not complete, but enough for you to see what they'll test."

Lin Chen took the note and unfolded it. On it were a few handwritten lines: HP8903B audio analyzer calibration. Oscilloscope trigger-mode setup. C-language pointer out-of-bounds debugging.

He stared at the last line. Pointer out-of-bounds. He had seen similar failures while dismantling and reassembling radios at the repair shop, but he had never written code. The information gap took concrete form once again. It was not a matter of intelligence. It was a matter of exposure.

He tucked the note into the ledger and closed it. The numbness in his left foot remained, but the scale marks in his mind had already been recalibrated.

After school that afternoon, Room 407 on the fourth floor. The key slid into the lock and turned. The door opened. Dust floated in the slanting sunlight, and the air smelled of old rosin and insulating varnish. He went in and set his canvas bag on the table. On the blackboard remained half a Fourier series from the previous year's students, the chalk writing already blurred.

He picked up a piece of chalk and wrote the first line of the formula in an empty space. Chalk dust settled on his fingertips. From outside the window came the sound of basketball on the athletic field, distant, as though muffled by a layer of water.

The ledger opened to a fresh page. Friday 18:00. Variable: Laplace. Cost: time.

What he did not know was that in Wednesday's first mock-exam room, the proctor would hand out the papers ten minutes early. And the Provincial Institute of Science and Engineering's verification notice would arrive on Tuesday afternoon, delivered by express post to the reception office of County No. 1 High School. Inside the envelope, along with the interview schedule, there would be an additional note: On the day of verification, please bring one independently completed project code file or circuit design drawing as reference for practical ability.

But at this moment, Lin Chen was only bent over his calculations. Chalk scraped across the blackboard with a dry rustle. The scale marks were still there. The tolerances would continue to be compressed.