This counter records the total number of errored seconds (ES) that occurred during a specific historical 15-minute interval in the past 24 hours, stored in an interval statistics table. By querying different interval numbers, operators can reconstruct when errors began, whether they were intermittent or continuous, and whether the problem is getting worse or better over the day. Historical interval data is crucial for troubleshooting because it lets you see patterns that might not be obvious from real-time counters alone.