This read-only value, bounded 1 to 96, identifies which specific historical 15-minute interval this row represents, where 1 is the most recently completed interval and 96 is the least recently completed (24 hours prior), assuming all 96 intervals are valid per dsx1ValidIntervals. This is the index that orders the historical performance table chronologically, letting an admin walk backward through the last 24 hours in 15-minute increments. An engineer investigating a specific outage timestamp from three hours ago would calculate which dsx1IntervalNumber corresponds to that time (roughly interval 12, since 3 hours / 15 minutes = 12 intervals ago) and pull that specific row's error counts.