2The value of the said activities for a rating area shall be an apportioned part of the aggregate value of the activities, and the apportionment shall be made—
(a)in the case of distribution activities, by reference to the aggregate net annual value of the rating area, or so much thereof as is comprised in the area of the Board, and of the area of the Board,
(b)in the case of generating activities, by reference to the generating capacity of the Board in the rating area and the aggregate generating capacity of the Board.