A number between 1 and 98, which identifies the
interval for which the set of statistics is available.
The interval identified by 1 is the ongoing, current
15 minute interval.
The interval identified by 2 is the most recently
completed 15 minute interval. The interval identified
by 97 is the oldest 15 minute interval. The interval
identified by 98 is a total of the previous 96 stored
15 minute intervals.