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 comes from the live 24-hour bin accumulating since the last daily roll-over 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, so far within today's still-open 24-hour interval.