Acoustic Signal Calibration

Morning light struck the varnished timber rail of the chair backrest. I unhooked my left hand from the sharpener harness to conduct sector sweep. Resting two inches east in the wood grain seam was an intact, yellow plastic thumbtack. I stepped forward, boots locked onto the narrow curve, and tested its conical head with both rigid palms. Dense plastic, sharp brass pin intact. Bracing my heels against the wood, I inverted the tack and wedged its brass shaft firmly into the sharpener blade gap. Tapping the plastic crown with my boot heel produced a sharp, resonant snap across the timber ridge. Early alert system calibrated.