10.17. In computing the annual earnings from a mine an operator operates for a fiscal year, the operator is required to deduct for the fiscal year, as a depreciation allowance in respect of class 1A property, class 2A property, class 3A property and class 4A property, under subparagraph b of subparagraph 2 of the fourth paragraph of section 8, an amount equal to the amount the operator deducted as such for the fiscal year in computing the mine-mouth output value in respect of the mine under subparagraph b of subparagraph 2 of the second paragraph of section 8.1.1.