156 4. Within a year of the date of commencement of commercial production, in conformity with paragraph 3, a contractor shall choose to make his financial contribution to the Authority by either: (a) paying a production charge only; or (b) paying a combination of a production charge and a share of net proceeds. 5. (a) If a contractor chooses to make his financial contribution to the Authority by paying a production charge only, it shall be fixed at a percentage of the market value of the processed metals produced from the polymetallic nodules recovered from the area covered by the contract. This percentage shall be fixed as follows: (i) years 1-10 of commercial production 5 per cent (ii) years 11 to the end of commercial production 12 per cent (b) The said market value shall be the product of the quantity of the processed metals produced from the polymetallic nodules extracted from the area covered by the contract and the average price for those metals during the relevant accounting year, as defined in paragraphs 7 and 8. 6. If a contractor chooses to make his financial contribution to the Authority by paying a combination of a production charge and a share of net proceeds, such payments shall be determined as follows: (a) The production charge shall be fixed at a percentage of the market value, determined in accordance with subpara-graph (b), of the processed metals produced from the polymetallic nodules recovered from the area covered by the contract. This percentage shall be fixed as follows: (i) first period of commercial production 2 per cent (ii) second period of commercial production 4 per cent If, in the second period of commercial production, as defined in subparagraph (d), the return on investment in any accounting year as defined in subparagraph (m) falls below 15 per cent as a result of the payment of the production charge at 4 per cent, the production charge shall be 2 per cent instead of 4 per cent in that accounting year. (b) The said market value shall be the product of the quantity of the processed metals produced from the polymetallic nodules recovered from the area covered by the contract and the average price for those metals during the relevant accounting year as defined in paragraphs 7 and 8. (c) (i) The Authority's share of net proceeds shall be taken out of that portion of the contractor's net proceeds which is attributable to the mining of the resources of the area covered by the contract, referred to hereinafter as attributable net proceeds. (ii) The Authority's share of attributable net proceeds shall be determined in accordance with the following incremental schedule: