Chapter 41: Voltage Stabilizers and Postmarks

5:50. The alarm had not gone off. His eyelids opened first.

Gray-white outside the window. Heavy frost in the air. He sat up. The edge of the gauze on the sole of his foot had curled. The crack had scabbed over. Dark red. He pressed it. No pain. Only tightness. He put on his shoes slowly. Shifted his weight to the outer edge. Avoided the pressure point. Pushed open the door. A thin layer of ice had formed on the terrazzo floor in the corridor. Wind poured in through the north window. It carried the smell of rust and old wood. He walked close to the wall. Light steps. In his canvas bag were the blank exam sheets he had cut last night. A ruler. A set square. Pencils. An eraser. No scratch paper. The rules were set. He could only adapt.

6:05. Laboratory building. West side of the first floor. The iron door was left ajar. Dim yellow light showed through from inside. Old Li wore a blue lab coat washed pale with age. He was bent over organizing the equipment cabinet. The sound of metal knocking together. Crisp. Lin Chen stood outside the door. Waited. Counted to thirty. Knocked twice. “Come in.” Old Li straightened up. Saw him. Was not surprised. “You’re here early.” Lin Chen nodded. “Teacher. I need to borrow a regulated power supply. Twelve-volt spec. An ammeter. A voltmeter. Wires. A switch.” Old Li sized him up once. His gaze dropped to Lin Chen’s foot. He did not ask. He turned and dragged out a wooden box from the bottom shelf of the cabinet. Dust covered the lid. He opened it. Everything inside was neatly arranged. The paint on the regulated power supply’s casing had chipped away. The scale on the knob was still clear. The binding posts looked new. Old Li picked out two ammeters. Two voltmeters. A sliding rheostat. A resistance box. Several bundles of wire. Set them on the table. “The internal resistance of the regulated supply can be ignored. Output stays constant. But the current limit is high. Pick the wrong range and you burn the meter on the spot. If you break it, you don’t pay for it. Put everything back where it belongs when you’re done. Don’t touch the high voltage.” Lin Chen thanked him. Reached out. His fingertips touched the metal terminal posts. Ice-cold. Rough. He hugged the wooden box tight, turned, went downstairs. His steps were steady.

6:20. Library basement. Abandoned reading room. The heat had been shut off. The air was hard with cold. He found a long table against the wall. The paint on its surface had flaked away. The scratches were deep. He laid out the equipment. Spread open the lab manual. Checked it against the circuit diagram. Began wiring.

Measuring resistance with the volt-ampere method. Switch the power source to 12V. The unknown resistor was about ten ohms. Estimated current: 1.2 amps. The original 0.6-amp range would overload. He had to switch to the 3-amp range. Or add a series protection resistor. He chose the latter. A fixed twenty-ohm resistor in series. Current limiting. The ammeter set to the 0.6-amp range. The voltmeter to the 15-volt range. Step three. Connect the circuit. Positive terminal of the supply. Switch. Sliding rheostat. Current-limiting configuration. Protection resistor. Ammeter. Unknown resistor. Voltmeter in parallel. Back to the negative terminal of the supply. He twisted the wires tight. Tightened the binding posts. The feel was stiff. The threads bit firmly. He used force. The pads of his fingers reddened. It held. The circuit was closed.

He pressed the switch. The needle jumped. Stopped at 0.21 amps. The voltmeter. Stopped at 2.1 volts. He recorded it. Broke the circuit. Changed the position of the rheostat slider. Measured again. Recorded again. Five times. The data lined up in the lower right corner of the blank exam sheet. The space was tiny. The handwriting had to stay compact. He drew coordinate axes. Plotted points. Drew the line. Calculated the slope. The pencil tip hovered. There was no scratch paper. All mental arithmetic had to happen in his head. 0.21 times 20. 4.2. 2.1 divided by 0.21. Ten. He wrote it down. Erased once. Crossed it out. Wrote again. 10.0. Second time. Third. Fourth. Fifth. Draw the line. Calculate the slope. Read the intercept. The page stayed neat. Two corrections. One left.

He stopped. Closed his eyes. His finger traced in the air over the tabletop. Replaying it in his mind. 12V regulated supply. Constant voltage. Current changing with external resistance. Range selection had to be calculated in advance. He could not rely on probing it by trial. Trial probing in a written test was a dead end. He opened his eyes. Adjusted his posture. Made his line of sight perpendicular to the meter face. Avoided looking down from above or up from below. Read the values again. 0.21 became 0.205. Estimated reading. Voltage 2.1 became 2.08. Fine-tuned the data. Recalculated the slope. 10.2. Smaller error.

He understood. The regulated supply was not a gift. It was a trap. High voltage. High current. Choose the wrong range and it was zero points, straight away. He continued. Measuring the power source’s electromotive force and internal resistance. U-I graph. Change the external resistance. Record six sets of data. The paper ran out of space. He could only calculate the plotting positions in his head and put down the marks directly. Point. Line. Slope. Intercept. Third correction. His pencil tip stopped. He could not cross anything out again. He changed angles, used the edge of the ruler to press lightly over the wrong number, and wrote the correct value beside it. Did not black it out. Did not cover it over. Left white space on the page. The rules allowed it. He wrote down, Page strategy: reserve a correction zone. Mental calculation first. Once the pencil lands, it’s fixed. 12V supply: decide the range in advance. Always add a protection resistor.

7:50. The bell for morning reading rang. He packed up the equipment. Coiled the wires neatly. Tightened the posts. Shut the wooden box firmly. Carried it back to the lab building. Old Li was smoking at the door. Saw him. Nodded. “Got the feel for it?” Lin Chen answered, “There was some deviation. I recorded it. Recalculated the ranges.” Old Li blew out a mouthful of smoke. “A regulated supply tests prediction. Not reaction. Remember that. Calculate accurately before you connect. Connect it wrong and they deduct everything. Get it right and the points are yours.” Lin Chen nodded. “Thank you, teacher.” He turned and went upstairs. His steps quickened. The crack on the sole of his foot rubbed inside the shoe. Pain came back. Like fine needles stabbing. He shifted his weight again, pressing the outside edge. Did not slow down.

7:50. Classroom. Morning reading. He sat down. Did not make a sound. Opened his physics mistake notebook. Started a new page. Wrote: Day 21. 07:55. 12V power supply deduction. The pencil tip paused. He made a list. One. Internal resistance of the 12V supply can be ignored. Voltage stays constant. Two. Range must be calculated in advance. Exceeding range means zero points at once. Three. Series protection resistor prevents the meter from burning out. Four. No scratch paper: three steps of mental calculation, one step on paper. Maximum of three corrections. Reserve a correction zone. Don’t chase completeness. Seize the core.

Four classes in the morning. Physics. Chemistry. Math. English. Lin Chen never looked up. His pencil kept moving. During breaks, he did not go into the corridor. He stayed in his seat. Eyes closed. Simulated building the circuit. 12V power source. Switch. Rheostat. Protection resistor. Meters. Unknown resistor. Connecting them in his mind. Direction of current. Voltage distribution. Needle deflection. Once. Twice. Three times. Muscle memory. He opened his eyes. On a blank sheet, he drew the U-I graph directly. No scale marks. Just plotted points. Drew the line. Found the slope. Mental calculation. Pencil down. Checked. No mistake. Time. 9:40. Twenty minutes before class resumed. He closed the notebook. His fingers tightened. The page edges curled. He stuffed it into the bottom of his bag and pinned it down.

Noon. Cafeteria. Clouds hung low. The wind was hard. Lin Chen waited until the end, avoiding the crowd, then walked to the long bench. Opened the oil-paper package. The rice was hard. The soup was cold. He broke up the rice and swallowed it with the soup. Something settled in his stomach. The crack on the sole of his foot kept rubbing inside his shoe. Every step a dull pain. He shifted his weight and pressed on the outside edge. The edge of the shoe sole had lifted. He pressed it flat with his fingernail. It would not go down. So he left it. Finished eating. Cleaned up. Left no trace.

Back to the classroom. Noon break. The room was half empty. Lin Chen did not sleep. He spread out the blank exam paper. Timed himself. Forty minutes. A mock winter camp experimental written test. No scratch paper. Limited corrections. Page counted in grading. He drew the table. Listed data. Calculated the slope. Found the intercept. Error analysis. Significant figures. The pencil made extremely fine lines on the paper. Even pressure. No shaking. Time up. He stopped writing. Checked against the answers. The approach was right. The calculations were right. Two corrections. The page was neat. But he had gone twelve minutes over the standard time. The bottleneck was time. No scratch paper. Heavy mental load. The steps had to be compressed to the extreme. He wrote down, Countermeasure: memorize common formula transformations. Modularize mental arithmetic. On paper, write only key steps and final results. Abandon long derivations.

2:00 p.m. Afternoon exercise period was canceled. He stayed in the classroom. Continued breaking down the motion-sickness medicine gap. Tuesday he had to go to No. 3 City High School. Two-hour ride. Mountain roads. Many bends. He got carsick. He had to prepare medicine. The school infirmary had Chengyunning. One box, six tablets. Price: eight mao. Funds: 1.56. Meal tickets: 0.32. Buy the medicine, 0.76 left. Don’t buy it, gamble on his body. He calculated the account. Motion sickness. Vomiting. Affects written-test condition. Poor condition. Lose points. Lose points. Fail. Fail, and everything before this goes to waste. Eight mao. Buy it. He stood up. Went to the infirmary. Lined up. Handed over the money. Took the medicine. Aluminum-plastic blister pack. White tablets. He stuffed it into the pocket against his body. His fingers tightened. The edge of the cloth packet bit into his palm.

3:10. He left the school grounds and walked toward the town post office. It was far. The sole of his foot hurt. He walked slowly. Pressed on the outside edge. Avoided the gravel. The post office’s wooden door was mottled with age. The glass window was covered with faded notices. He pushed the door open. The hinge creaked. Behind the counter sat an old postal worker. Wearing reading glasses. Flipping through letters. Lin Chen stepped forward. “Sir. I’m checking on a letter. Lin Jianguo of Qingshi Village. Financial aid application form. Mailed four days ago.” The old postal worker looked up. Flipped through the register. Wet his finger with saliva and turned the pages. Stopped. “Qingshi Village. Yes. It arrived at the town sorting station yesterday. It goes out today. But the road into the village is cut off. Tractor can’t get through. You’ll have to wait until tomorrow.” Lin Chen nodded. “Thank you.” He turned and went out. The wind was cold. He stood on the steps. Wait until tomorrow. That meant the materials might miss the Friday deadline. Margin for error: zero. He could not wait. He walked back to school. Found the homeroom teacher. Explained the situation. The teacher frowned. “Postal delay. The school is not responsible. Figure it out yourself. Or have the village issue a certificate and deliver it directly to the county education bureau.” Lin Chen nodded. Wrote it down. Certificate. Tractor. County education bureau. Long route. Time-consuming. But possible. He returned to the classroom, sat down, and moved his pencil across the paper. Postal route cut off. Backup plan: village certificate. Borrow a tractor. Deliver to county education bureau Saturday morning. Needs coordination.

Evening self-study. 18:30. The classroom was full. The fluorescent tubes hummed. The air smelled of old books and sweat. Lin Chen finished that day’s homework. Closed the exercise book. Looked at the clock. 21:10. Twenty minutes until lights-out. He packed his schoolbag. Counted the cardboard backing, pencils, eraser, ruler, set square, one by one. Put them into the canvas bag. Zipped it shut. No candles left. He would use the corridor emergency light instead.

21:30. The lights-out bell rang. The corridor went dark at once. Chaotic footsteps. Washing sounds. Voices. Lin Chen waited. Counted to a hundred. The sounds thinned out. He pushed open the door and walked close to the wall. At the end of the corridor, the emergency light was on. Dim yellow. Blurred around the edges of the halo. He crouched down, back against the wall, out of the wind’s path. Opened his English vocabulary book. Timed. Ten minutes. Memorize only twenty words. Don’t be greedy. Aim for mastery. His pencil moved across the page. Copying. Phonetic symbols. Part of speech. Example sentence. Not one omitted. The light was dim. The handwriting small. He leaned in close. His eyes turned sore. Blinked. Continued. Checked the time. Nine minutes. One minute left. Check. Spelling. Correct. He closed the book. His fingers were numb with cold. His joints felt stiff. He hugged the canvas bag to his chest and stood up. His knees gave a faint crack. The pain in the sole of his foot had turned into a dull ache. Like a needle lodged in the ends of his nerves. He walked back to the fourth floor step by step. Pushed open the door. The dormitory was quiet. Only the even sound of breathing.

He walked to the bedside. Sat down. Took off his shoe. Untied the gauze. The edges of the crack were pale white. Tissue fluid had seeped out. No pus. He picked up the mercurochrome. A cotton swab. Dipped it. Applied it. Sharp pain. He held his breath. Spread it evenly. Rebandaged it. His movements were very slow. But extremely steady. He lay down. Closed his eyes. In his mind he arranged the timetable. Tomorrow. 6:30. Morning reading. Read aloud. 7:00. Breakfast. 8:00. Class. 12:00. Noon break. 18:30. Evening self-study. 21:30. Back to the dorm. Wash up. Sleep. One step, one imprint.

He felt for the account book. Opened it. The pencil moved. Day 21. 22:15. 12V power supply deduction completed. Second round of no-scratch-paper simulation. Progress: recalculated ranges in the electricity module. Protection-resistor strategy established. English vocabulary Section C advanced 40%. Motion-sickness medicine purchased (0.8 yuan). Postal delay confirmed. Time spent: all day. Status: on target. Gap: funds 0.76. Meal tickets 0.32. Foot injury not healed. Postal backup plan pending execution. New variable: advance range calculation for the 12V supply increases time cost. No-scratch-paper mental calculation compressed to 12 minutes over standard. Postal route cut off. Need village certificate + tractor to deliver to county education bureau. Countermeasure: tomorrow at 6:00. Library. Compress mental-calculation steps for the 12V supply. Draft village certificate at the same time. Funding gap: not handling for now. Protect the written test.

The pencil tip paused. He closed the account book. His fingers tightened. The edges of the pages curled. He shoved it into the bottom of his bag and pressed it down. Footsteps came from the corridor. Very light. Even rhythm. The night-duty teacher. A flashlight beam swept past the crack of the door. Stopped. “Sleep early. Final exams in twenty-four days. Don’t stay up too late.” The voice was low, echoing slightly. “Got it,” the boy in the lower bunk answered vaguely. Lin Chen made no sound. His hands rested on his knees, moving slowly. The pain in the sole of his foot had gone numb. His body felt hollowed out. But he did not sleep. Outside the window, the clouds had scattered. The moonlight was cold. Puddles reflected the light. The wind had stopped.

He slipped his hand into the pocket against his body and touched the notice stamped in red. The paper was warm. The edges curled. He unfolded it. Read it once. Registration. The time had changed. The rules remained. One step, one imprint. No disorder. He folded it. Put it away. His fingers tightened. The edge of the cloth packet bit into his palm. Closed his eyes. His breathing steadied. In his mind he arranged the timetable. Tomorrow. 6:30. Morning reading. Read aloud. 7:00. Breakfast. 8:00. Class. 12:00. Noon break. 18:30. Evening self-study. 21:30. Back to the dorm. Wash up. Sleep. One step, one imprint.

The wind outside slipped through the cracks, making a low whistle. Far away, a faint broadcast drifted over. The county No. 1 High School campus radio. Sound check. Static. Then the dean’s voice. “Notice. Final confirmation from the Academic Affairs Office of No. 3 City High School. The assembly time for the winter camp written test has been moved to 5:30 Tuesday morning. The test site gate will open promptly at 6:00. Late arrivals will be disqualified. Also, due to recent rain and snow, mountain roads are slippery. Candidates are advised to bring their own anti-slip shoe covers. The school will provide a rented vehicle at no extra charge.”

The sound spread through the night wind. Hard and metallic.

Lin Chen opened his eyes. His gaze fell on the account book by the bed. The page looked pale. He reached out. Found the pencil. Drew a very light line across the blank page.

Day 21. End. Progress: adapted to the 12V power supply. Postal backup plan established. Status: alive. New variable: assembly time moved up to 5:30. Must depart before dawn. Gap: anti-slip shoe covers. Foot injury risk doubles on wet, slippery roads. Countermeasure: tomorrow during break. Ask Old Li to lend an old pair of rain boots. Contact the village head at the same time to issue the certificate. Funding gap: needs assessment.

The pencil tip paused. He set it down. Closed his eyes.

Tomorrow. Six o’clock. Library.

He turned over, facing the wall. His breathing slowed. His fingers unconsciously rubbed the zipper pull on the canvas bag. The metal was cold. Rough. Like an unpolished stone. He closed his eyes. There were no formulas in his mind. No words. Only two numbers. Tuesday. Dawn. Five-thirty. Two lines crossing in the dark. Not colliding. Not entangling. Each moving forward on its own. Night dew condensed. On the window glass. A thin layer of frost formed.