Acoustic Signal Calibration

Advancing past the yellow pencil, I encountered a transparent glass marble resting in a natural groove in the shelf timber. The sphere rolled slightly when tested with my left boot. To prevent uncontrolled movement across the patrol deck, I nudged the sphere toward a small brass screw set into the side upright. It settled against the metal head with a sharp, distinct chime. Striking the curved glass with my blaster stock confirmed that high-frequency sound carries along the entire length of the book row. The acoustic tripwire is positioned and operational.