Chapter 58: Zero Point and Waveform

08:42. Corridor. Terrazzo floor. A thin skin of frost crusted over it. Soles scraping. A fine, brittle rustle. The air was hard with cold, carrying the lime smell of old plaster peeling from the walls, mixed with coal smoke drifting from the boiler room in the distance. Lin Chen’s stride was thirty centimeters. Weight shifted right. Left foot suspended. Not pressing on the scab. The canvas bag strap bit into his shoulder blade. Weight evenly distributed. He breathed. White mist scattered.

The laboratory’s iron door stood slightly ajar. A faint instrument glow leaked through the crack. Orange-red. Steady. He pushed the door open. Cold air hit him full in the face. The windowpanes were furred with frost flowers. Sunlight slanted in, and the dust drifting through the beam was sharply visible. Group A students were already in place. Fifteen lab benches arranged in a U. Anti-static rubber mats covered the tops, their edges curling. Some rubbed their hands together. Some flipped through notes. Others spoke in low voices. Chen Hao sat in the middle of the front row. His equipment was already powered on. Probe leads straightened. The oscilloscope screen lit up, green graticule, no flicker. He sat upright, fingers resting on the knobs, waiting.

Lin Chen walked to the corner. Third bench. He set down his canvas bag. Unzipped it. Metal clasps clicked together, sharp and clear. He took out the equipment case. Opened it. The catches sprang loose. Oscilloscope. Probes. Signal generator. Multimeter. Basic component kit. Everything arranged in order. He counted them. Checked them against the list. Ticked them off one by one. No mistakes.

08:55. He sat down. Didn’t touch the knobs. Looked first. Instruments. Warm-up. Three minutes. He waited. His finger traced invisible lines across the tabletop. Circuit diagram. Signal source. Output. Voltage divider. RC phase-shift network. Oscilloscope. X-Y mode. Common ground. Critical. Stray capacitance, about 15 pF. Temperature drift. Compensation required. He closed his eyes. There was no anxiety in his mind. Only parameters. Formulas. Paths. Three lines crossing in the dark. Not colliding. Not tangling. Each moving forward.

09:00. Old Li pushed the door open. Army coat. Collar turned up. Chalk dust on his shoulders. He rapped the blackboard three times. The chalk snapped. White dust drifted down.

“Practical evaluation. Forty-five-minute limit. Task: use the oscilloscope and a Lissajous figure to measure phase difference. Input signal: 1 kHz. Sine wave. Reference signal: same frequency. Phase shift. Record the X-axis and Y-axis deflection ratio. Calculate the phase angle. Allowed error: plus or minus three degrees. Go overtime, zero points. Wire it wrong, short it out, and you’re out immediately. Begin.”

The stopwatch ticked. Metal case. Catching the light.

Lin Chen got to work. Wiring. Banana plugs pushed into the sockets. Tight. No looseness. Lead order. Red. Black. No crossing. Power on. Indicator light lit. He adjusted the signal generator. Frequency: 1000 Hz. Amplitude: 2 Vpp. Waveform: sine. Stable. He connected the RC network. Resistor: 1 kΩ. Capacitor: short by 365 pF. He took out substitute components: two 100 pF ceramic capacitors, paralleled, then in series with a 50 pF trimmer capacitor. He calculated. Equivalent capacitance: 350 pF. Add the stray capacitance, about 15 pF. Close enough. He turned the trimmer. The knob’s damping was sticky. He applied force evenly, without stripping it. His fingertips felt the resistance change. Half a turn. Stop.

He connected the oscilloscope. Channel one: reference. Channel two: phase-shifted signal. Mode: X-Y. He adjusted the knobs. A bright point appeared, then an ellipse, tilted. He watched the screen. Green phosphor. Steady. No flicker. He adjusted vertical gain, horizontal gain. Centered the ellipse. Let it fill three-quarters of the display without overflowing. He read the values. X-axis intercept: 2 divisions. Y-axis maximum: 4 divisions. Formula: arcsin(X/Y). Calculation: 30 degrees. Theoretical value: 30 degrees. Error: zero.

He wrote it down. Pen on paper. Numbers clear. No crossings-out.

He kept going. Changed the frequency. 2 kHz. 500 Hz. Repeated the process. Wiring. Adjustment. Readings. Recording. Muscle memory. Not relying on his eyes, but on touch. Knobs. Damping. Feedback. Fingertips sensing minute changes. Fine adjustment. Compensation. Stray capacitance. Temperature drift. He calculated. Corrected. Kept the error within one degree.

Twenty minutes in. The scab on his left foot split open. A stabbing pain. Blood seeped through. The gauze grew faintly damp, sticking to the skin. He ignored it. Shifted his weight right. Didn’t press down. Breathing steady. White mist scattered. His fingers were stiff with cold, knuckles gone pale. He breathed into them. White mist scattered. Continued.

Thirty-five minutes in, Chen Hao raised his hand and handed in his paper. He stood and left. His footsteps were light. Confident. Door open. Door shut. A gust of wind poured in. Cold.

Lin Chen didn’t look up. Kept working. Measuring. Third set of data. Recorded. Checked. Formula. Verification. No mistakes. He checked the wiring. No looseness. No short. Probe ground clip biting tight. Metal teeth sunk into the rubber insulation. No slipping.

At forty-four minutes, he put down his pen. Powered off. Removed the leads. Straightened the tabletop. No clutter. Sorted the wires. Returned the instruments to their places. Knobs back to zero. Probes coiled and secured.

He stood and handed in his paper. Flat. Neat. Held it out.

Old Li took it. Looked. Three sets of data. Errors: 0.8 degrees, 1.2 degrees, 0.5 degrees. He raised his head and looked at Lin Chen. Dark circles under his eyes. Cracked lips. Chilblains purpled by the cold. But his hands were steady. No tremor. Rosin and copper oxide under his fingernails.

“What did you use for the substitute capacitor?”

“Ceramic discs. In parallel. Added a trimmer. Compensated for stray capacitance.”

“How’d you calculate it?”

“Equivalent capacitance formula. Added it up. Then corrected against the measured value. Error stayed within tolerance.”

Old Li nodded. Neither praise nor criticism. “Sit down. Wait for the results.”

The lab went quiet. Only the stopwatch ticking, and the faint hum of cooling fans inside the instruments. The smell of rosin gradually thickened in the air.

Forty-five minutes. Up. Old Li collected the papers. Checked them. Scored them. Chalk scratched across the blackboard as he wrote the rankings in broad, heavy strokes.

Group A. Fifteen students. Lin Chen, first. Chen Hao, second. Third through fifteenth, in order.

Old Li turned around. “Evaluation over. Rankings posted. Top three advance to the intensive group. The other twelve are eliminated and sent back to their original schools. Tomorrow, the intensive group assignments will be announced. Lab assistant positions. Stipend: eight yuan a day. Meals included, three a day. But you still have to pass a practical review. Fail that, and it’s canceled.”

He paused, his gaze sweeping to Lin Chen. “Lin Chen, stay for the review. Everyone else, dismissed.”

The students stood. Packed up. Left. Footsteps mingled. Door open. Door shut. Wind poured in. Cold.

Only two people remained in the lab. Old Li walked to Lin Chen’s bench and set down an old oscilloscope in front of him. The casing was deeply scratched. Screen dark. Knobs loose. Domestic model, made in 1985. CRT aging. High-voltage transformer leaking. Power filter capacitor bulging.

“The school scrapped three of these,” Old Li said. “If you can fix them, fix them. Twenty yuan cash for every one you get working. Paid on the spot. Fail, and you work for nothing. Bring your own tools. Parts can be signed out from the storeroom. Time limit: two hours. Start.”

Lin Chen looked at the machine. Reached out. Touched the casing. Cold, but carrying a faint vibration. Powered test. He didn’t hesitate. Opened his bag. Took out his tools. Screwdriver. Multimeter. Soldering iron. Rosin. Solder. Electrical tape.

He opened the case. The screws were rusted, hard to turn. He applied more force, steady, no slipping. The casing came off. Thick dust inside. Circuit board yellowed. Oxidized solder joints blackened. He measured the power output. Twelve volts. Normal. The high-voltage transformer was leaking. He removed it. Replaced it. Bent the new leads into position. Secured them. Heated with the soldering iron. Fed in solder. Pulled away. The joints came out full and smooth, no burrs.

The CRT was aging. He adjusted the focus potentiometer. The knob was stiff. He turned it with even pressure, without stripping it. The screen lit. The graticule steadied. No flicker. He adjusted brightness and contrast. The waveform came out clear. No distortion.

One hour twenty minutes in, he reassembled the case. Closed it. Tightened the screws. Powered it on. Tested it. Signal in. Waveform stable. Phase accurate.

He stood and handed over the machine.

Old Li looked at the screen. Nodded. “All right. Twenty yuan. Cash.” He took out the money. The notes were old, but flat and neat. Held them out.

Lin Chen took them and slipped them into the inner pocket against his body. His fingers brushed the curled edge of his ledger. Coarse paper rasped against his skin.

Old Li said, “Tomorrow, eight o’clock. Assemble at the lab. Intensive group assignment: high-frequency module tuning. Late means eliminated.”

“Understood.”

Lin Chen slung the canvas bag over his shoulder and walked out. The corridor was empty. His footsteps struck the terrazzo, echoes short and cold.

He touched the money in his pocket. Twenty yuan, plus the previous twenty-five, plus meal tickets converted to cash, one point five. Total: forty-six point five. The gap: seventy-five. Still short by twenty-eight point five.

He wasn’t anxious. In his mind there were only calculations. Paths. Countermeasures. Time. Windows of opportunity. Limits of physical strength. Three lines crossing in the dark. Not colliding. Not tangling. Each moving forward.

He walked. Thirty-centimeter stride. Not stepping on the frost line.

Ahead, a new notice had been posted on the bulletin board. White paper. Black characters.

University library. Recruitment for temporary workers to sort old books. Piece-rate pay. Five yuan per hundred volumes. Limited slots. Tomorrow morning.

He stopped and looked. Five yuan per hundred. Heavy work. But steady.

He memorized the time. The place. The route.

He turned and headed back to the dormitory. Wind passed through the corridor with a low whistle.

He closed his eyes. In his mind there were no curves now. Only solder joints. Temperature. Time. Melted solder. Solidification. Three lines crossing in the dark. Not colliding. Not tangling. Each moving forward.

He opened his eyes. Thirty-centimeter stride. Not stepping on the frost line.

Forward.