This counts the one-second intervals during the bin in which at least one coding violation was detected on this OTU signal. Because this reading sits in the rolling window of completed 15-minute history bins for this OTU signal, Errored Seconds is the standard telecom metric SLAs are written against, so this count on this specific OTU signal is often what actually determines whether a service-level threshold was breached this bin. For example, a bin with 3 Errored Seconds out of 900 seconds (a 15-minute interval) is well within most carrier-grade SLAs, whereas the same OTU signal logging 120 ES in one bin would likely breach a typical 99.999%-availability commitment, within that completed 15-minute window.