cmBoardIndex is a read-only integer that uniquely identifies a single row in the board table, distinguishing one physical card in the chassis from every other. An administrator uses it as the key to correlate other board-table columns, such as cmBoardOperState or cmBoardSerialNumber, back to a specific physical slot. For example, when a trap reports a fault against a given cmBoardIndex value, the operator looks up that same index in the table to find the board's cmBoardSerialNumber and know exactly which card to pull.