157 Portion of attributable net proceeds That portion representing a return on investment which is greater than 0 per cent, but less than 10 per cent That portion representing a return on investment which is 10 per cent or greater, but less than 20 per cent That portion representing a return on investment which is 20 per cent or greater (d) Share of the Authority First period of commercial production Second period of commercial production 35 per cent 40 per cent 42.5 per cent 50 per cent 50 per cent 70 per cent (i) The first period of commercial production referred to in subparagraphs (a) and (c) shall commence in the first accounting year of commercial production and terminate in the accounting year in which the contractor's development costs with interest on the unrecovered portion thereof are fully recovered by his cash surplus, as follows: In the first accounting year during which development costs are incurred, unrecovered development costs shall equal the development costs less cash surplus in that year. In each subsequent accounting year, unrecovered development costs shall equal the unrecovered development costs at the end of the preceding accounting year, plus interest thereon at the rate of 10 per cent per annum, plus development costs incurred in the current accounting year and less contractor's cash surplus in the current accounting year. The accounting year in which unrecovered development costs become zero for the first time shall be the accounting year in which the contractor's development costs with interest on the unrecovered portion thereof are fully recovered by his cash surplus. The contractor's cash surplus in any accounting year shall be his gross proceeds less his operating costs and less his payments to the Authority under subparagraph (c). (ii) The second period of commercial production shall commence in the accounting year following the termination of the first period of commercial production and shall continue until the end of the contract. (e) "Attributable net proceeds" means the product of the contractor's net proceeds and the ratio of the development costs in the mining sector to the contractor's development costs. If the contractor engages in mining, transporting polymetallic nodules and production primarily of three processed metals,