This read-only integer, from 1 to 96, indexes a specific historical 15-minute interval in the link's rolling 24-hour performance table, with 1 being the most recently completed interval and 96 the oldest still retained. A manager uses this index to select which past interval's ES, SES, BER, and RSL figures to pull when investigating a specific past time window. For example, requesting interval number 4 would retrieve the performance figures from roughly an hour ago, letting an operator narrow down when a since-cleared alarm actually occurred.