Acoustic Tuning

A smooth glass marble sat trapped in the iron slot of the drain cover. It rattled erratically with every footstep nearby. Uncalibrated frequency. I knelt on the cold flagstone, locked both knee ratchets, and squared my shoulders. I aligned my right heavy gauntlet over the sphere. One measured knuckle tap. Clack! The marble dropped straight through the slot, striking the metal baffle four inches below with a sharp, resonant chime. Pure mechanical tone. Zero erratic vibration remains.