This counter reports the number of line-level Errored Seconds on this T1/DS1 port, as stated in the MIB description. Each increment means a full one-second interval within this 15-minute bin contained at least one line-level error, so this figure -- read as a fraction of the bin's total seconds -- is the standard T1 metric carriers use to judge whether a circuit meets its error-rate SLA. For example, 45 errored seconds out of the 900 seconds in this bin puts the circuit's error-second ratio at roughly 5.0%, which an admin would compare against the carrier's contracted threshold for that circuit.