Chapter 90: Filling and Margin

At nine sharp, the bell cuts through the air. The invigilator’s voice falls away. Lin Chen’s pen touches paper. First question: Kirchhoff’s Current Law. The algebraic sum of currents at a node is zero. Option A. He fills it in. Second question: series resonance in an RLC circuit. Calculation of the quality factor Q. Substitute into the formula. Check the result. Fill it in. The rhythm is fixed. Neither hurried nor dragging. Time is sliced into segments of equal length. Every fifteen minutes, he lifts his head once to look at the wall clock. The second hand jumps forward. Beneath the dressing, the dull pain in his left foot begins to throb with regular force, like another heart. He adjusts his posture. Lets his center of gravity shift slightly to the right, easing the load on the left leg. His breathing stays at twelve cycles a minute. His brain handles only input and output. The questions are signals. The pen tip is the actuator. No emotion interferes in between.

He is past the halfway point in the multiple-choice section now, entering fill-in-the-blank and short-answer questions. Question Three: derive the boundary conditions of the electromagnetic field. He writes out the integral form of Maxwell’s equations. Tangential continuity at the boundary. A jump in the normal component. The steps are clear. His handwriting is neat. No joining of strokes. No corrections. The scratch paper has been folded three times and divided into zones. Calculations on the left. Verification on the right. Question Four: Fourier-series expansion. Periodic signal. Odd function. Sine terms only. He writes down the coefficient integral. The calculations are tedious, dense with numbers. He slows his pace and checks each digit one by one. Three places after the decimal point. Error kept within five-thousandths. This is the provincial supplemental theory exam for electronic information, not the college entrance examination. The tolerance for error is lower. But the rules are more transparent. He does not need to guess the examiner’s intent. He only needs to answer to the laws of physics.

At eleven-twenty, forty minutes remain before the papers are collected. His stomach begins to contract. The half bun from morning has long since been burned away. The dizziness of low blood sugar rises in a light wave. He stops writing. Closes his eyes. Takes three deep breaths. Presses the tip of his tongue to the roof of his mouth. Saliva forms, easing the dryness. The seepage from his left foot worsens. The edge of the gauze is already soaked through. The sticky adhesion is obvious. He cannot move. The discipline in the exam room is strict; any large movement will draw the invigilator’s attention. So he stays still, classifies the pain as background noise, and keeps answering. The final comprehensive question: the principles of the spectrum analyzer and error analysis. HP8591E. Intermediate-frequency bandwidth. Resolution bandwidth. Sweep time. He knows these parameters well. The charts from the manual unfold in his mind. He writes out the calibration formula, plugs in the 10 dB attenuation step, and calculates the dynamic range. The pen moves smoothly, without a snag.

At eleven-fifty-five, the warning bell for hand-in rings. He sets down his pen and scans the answer sheet quickly from top to bottom. Every bubble filled. No omissions. No misalignment. Name. Admission-ticket number. Seat number. All checked and correct. He raises his hand. The invigilator comes over. Collects the paper. Seals it. The process is over. He stands. His left foot touches the floor. The stabbing pain flares at once. He clenches his back teeth and walks out of the classroom in thirty-centimeter strides. The corridor is crowded with students. Voices comparing answers. Sighs. Complaints. He keeps his head down, avoids the flow of people, and walks along the base of the wall. He does not look back. He does not speak. His battlefield is not here. It is in tomorrow’s practical lab.

Back at the guesthouse. Third floor. The corridor is dim. The key turns. The door opens. A musty smell rushes at him. He sets down his backpack and takes off his shoe. The gauze on his left foot is completely soaked, tissue fluid mixed with iodine, the edges hardened stiff. He cuts away the dressing. The wound surface is whitish. No suppuration. But the skin is fragile. He rinses it with saline, then uses a cotton swab to dry it with the lightest touch, careful not to tear the newly formed tissue. He bandages it again. Compression fixed. He stands, pours water, and gnaws at the remaining half of the steamed bun with pickled vegetables. Chews. Swallows. Energy restored. Account balance: seven yuan and thirty mao. He takes out his notebook, flips to the page for the practical supplemental exam, and writes: Theory completed. Entering the preparation phase for practical review.

At two in the afternoon, he goes to the bulletin board at the exam site. The rules for the practical exam have been posted. Entry tomorrow at eight. Exam starts at eight-thirty. Equipment list confirmed: one HP8591E spectrum analyzer. One signal generator. One oscilloscope. One multimeter. One standard attenuator set. Provided by the exam site. Personal equipment prohibited. Warm-up time: fifteen minutes. Cold start. Supply voltage 220V plus or minus ten percent. He records every word. He circles cold start and personal equipment prohibited. That means the homemade attenuator he built cannot be brought in. He will have to rely entirely on the site’s equipment. The resistance of the manual knobs is unknown. The precision of the scale markings is unknown. He must adapt in advance—or accept the error.

He returns to his room and opens his notebook of mistakes. He cross-references the common errors on the theory paper with the parameters of the practical exam, establishing a mapping between them. Time. Voltage. Frequency. Attenuation. Everything quantified. He calculates how to allocate his energy. The practical exam requires him to operate while standing and to move around often. The load time on his left foot will exceed that of the theory exam. He adjusts his gait contingency plan: frequency of weight shifts, use of rest intervals. Every detail goes onto the list. Outside the window, the sky darkens. Neon lights come on across the provincial capital. A distant train whistle sounds. He closes the notebook, turns out the light, and lies down. The iron bed frame gives a faint groan. He regulates his breathing, slowing the rhythm. There is nothing in his mind about victory or defeat tomorrow. Only scales. Knobs. Needles. Current. Every variable has been entered. It is only waiting for engagement.

Late at night, footsteps echo in the corridor. They stop next door. Low voices seep through the thin wall. “The practical scoring criteria changed. Manual calibration is worth forty points. Any error above 0.5 dB gets points deducted immediately.” The voices fade away. Lin Chen opens his eyes. His fingers tighten unconsciously. Zero point five dB. The margin for error in the manual knob has been compressed to the limit. He sits up and switches on his flashlight. The beam falls across the notebook of mistakes. He picks up a pen and adds a line beneath Plan C: If the damping is too heavy, use segmented approximation. If the scale markings are blurred, rely on the oscilloscope waveform to infer it in reverse. The pen tip pauses. The ink dries. Outside, the night wind threads through the buildings with a low, hollow howl, like some kind of countdown. He closes his eyes and waits for daybreak.