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(2) The Minister shall compute the compensation for a power development on the basis of the figure previously fixed in accordance with section 19 as the actual cost of the development, adjust this figure so as to make allowance for any variation in the purchasing power of the dollar as shown by the official trade index or other official statistics most applicable to the case, and deduct an amount equivalent to the actual loss in value of the works due to their physical or functional depreciation or to other causes.
