This read-only integer, constrained to 1 through 96, is the table index that identifies one specific row of metered-outlet information within a Rack PDU. An admin doesn't set this value directly but uses it to walk the outlet info table and correlate other outlet attributes, like name or rating, to the same physical outlet. For example, an SNMP poller reading index 12 would then read the corresponding module index, number, and rating entries that all share that same row.