This value identifies the sub-slot number, 0 to 255, of a card that has further subdivisions within a chassis slot, and is included alongside hw52DevSlotNum in port up/down traps. Admins use it to pinpoint the exact sub-module on a multi-sub-slot line card generating an event. A port-up trap carrying sub-slot number 2 tells the admin the affected port sits on the second sub-module within that slot.