This counter tracks the number of Errored Seconds — seconds containing at least one Section-layer coding violation or defect — accumulated during the current 15-minute interval on this SONET/SDH Section. An admin cares because a rising ES count at the Section layer (the lowest SONET layer, covering the physical regenerator-to-regenerator span) indicates a physical-layer problem like a marginal optical link or connector, distinct from higher-layer path or line issues. For example, an ES count climbing steadily every time this counter is polled points to an ongoing physical transmission problem on this specific span rather than an intermittent one-off glitch.