Chapter 90: Filling and Margin

Nine o'clock sharp. The bell slices through the air. The invigilator’s voice falls silent. Lin Chen’s pen tip meets the paper. First question: Kirchhoff’s Current Law. The algebraic sum of currents at a node equals zero. Option A. Fill it in. Second question: RLC series resonance. Calculation of the quality factor Q. Plug into the formula. Verify. Fill it in. The rhythm is fixed. Not rushed. Not dragged. Time is carved into equal segments. Every fifteen minutes, he lifts his head. Checks the wall clock. The second hand ticks. The dull pain beneath the dressing on his left foot begins to pulse rhythmically. Like a second heart. He adjusts his posture. Shifts his center of gravity slightly to the right. Reduces the load on his left leg. Breathing held at twelve cycles per minute. His brain processes only input and output. The questions are signals. The pen tip is the actuator. There is no emotional interference in between.

Multiple choice is past the halfway mark. Moving into fill-in-the-blanks and short answers. Third major question: Derivation of electromagnetic field boundary conditions. He writes the integral form of Maxwell’s equations. Tangential components continuous. Normal components discontinuous. Steps are clear. Handwriting is neat. No cursive. No corrections. Scratch paper folded three times. Zoned for use. Left side for calculations. Right side for verification. Fourth major question: Fourier series expansion. Periodic signal. Odd function. Contains only sine terms. He writes out the coefficient integral formula. The calculation process is tedious. Numbers are dense. He slows his pace. Checks digit by digit. Retains three decimal places. Keeps error within five per thousand. This is a provincial competition. Not the college entrance exam. The fault tolerance is lower. But the rules are more transparent. He doesn’t need to guess the examiners’ intentions. He only needs to answer to the laws of physics.

Eleven twenty. Forty minutes remain until submission. His stomach begins to contract. The half steamed bun from morning has long been burned away. A faint dizziness from low blood sugar rises. He stops writing. Closes his eyes. Takes three deep breaths. Presses the tip of his tongue against his palate. Saliva secretes. Relieves the dry mouth. Exudation from his left foot worsens. The edge of the gauze is already soaked through. A distinct sticky sensation. He cannot move. Exam discipline is strict. Any large movement will draw the invigilator’s attention. He remains still. Classifies the pain as background noise. Continues answering. The final comprehensive question: Spectrum analyzer principles and error analysis. HP8591E. Intermediate frequency bandwidth. Resolution bandwidth. Sweep time. He is familiar with these parameters. The charts from the manual unfold in his mind. He writes the calibration formula. Plugs in the 10 dB attenuation step. Calculates the dynamic range. The pen tip flows smoothly. No hesitation.

Eleven fifty-five. The pre-submission bell rings. He sets down his pen. Quickly scans the answer sheet from top to bottom. All bubbles filled. No omissions. No misalignments. Name. Admission ticket number. Seat number. Verified correct. He raises his hand. The invigilator approaches. Collects the paper. Seals it. The process ends. He stands. His left foot touches the floor. The stinging pain instantly amplifies. He clenches his back molars. Takes thirty-centimeter strides. Walks out of the classroom. The corridor is surging with people. Voices comparing answers. Sighs. Complaints. He lowers his head. Avoids the crowd. Walks along the base of the wall. Does not look back. 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 hits him in the face. He drops his backpack. Takes off his shoe. The gauze on his left foot is completely saturated. Tissue fluid mixed with iodophor. The edges have hardened. He cuts away the dressing. The wound bed is pale. No pus. But the epidermis is fragile. He rinses it with saline. Gently pats it dry with a cotton swab. Movements extremely light. Avoids tearing the newly formed tissue. Re-bandages. Applies pressure fixation. Stands up. Pours water. Gnaws on the remaining half of the steamed bun. Pickled vegetables. Chews. Swallows. Energy replenished. Account balance: 7.3 yuan. He takes out his notebook. Flips to the provincial competition practical exam page. Writes: Theory exam concluded. Entering practical preparation phase.

Two o’clock in the afternoon. He heads to the exam site bulletin board. The practical exam rules 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. Standard attenuator set. Provided by the exam site. Personal equipment strictly prohibited. Warm-up time: fifteen minutes. Cold start. Supply voltage: 220V ±10%. He records every word. Circles cold start and personal equipment prohibited. This means his homemade attenuator cannot be brought in. He must rely entirely on the venue’s equipment. The damping feel of the manual knobs is unknown. The scale precision is unknown. He must adapt in advance. Or, accept the error.

He returns to his room. Opens his error log. Cross-references the theory exam’s common pitfalls with the practical parameters. Builds a mapping. Time. Voltage. Frequency. Attenuation. All quantified. He calculates his energy distribution. The practical exam requires standing operation. Frequent movement. The load time on his left foot will exceed that of the theory exam. He adjusts his gait contingency plan. Frequency of weight shifts. Utilization of rest intervals. Everything written onto the list. Outside, the sky darkens. The provincial city’s neon lights flicker on. A train whistle echoes in the distance. He closes the notebook. Turns off the light. Lies down. The iron bed frame emits a faint groan. He regulates his breathing. Slows the rhythm. His mind holds no thoughts of tomorrow’s victory or defeat. Only scales. Knobs. Pointers. Current. All variables have been logged. Awaiting engagement.

Late night. Footsteps echo in the corridor. Stop next door. Whispers seep through the thin wall. The practical scoring criteria changed. Manual calibration is worth forty points. Errors exceeding 0.5 dB will be penalized directly. The voices fade. Lin Chen opens his eyes. His fingers unconsciously tighten. 0.5 dB. The tolerance margin for the manual knobs has been compressed to the absolute limit. He sits up. Turns on his flashlight. The beam falls on the error log. He picks up a pen. Adds a line beneath Plan C: If damping is too heavy, use segmented approximation. If scales are blurry, rely on oscilloscope waveforms for reverse deduction. The pen pauses. The ink dries. Outside, the night wind threads through the buildings. A low, hollow howl. Like a countdown. He closes his eyes. Waits for dawn.