The final question that arises under s. 122 is what divisor was to be taken for the purpose of applying sub-s. (2) of that section. ICI estimated the life of the mine as at 30th September 1967 as thirteen years but the Commissioner submitted that ICI had failed to make good this estimate and that twenty-five years should therefore be taken as the divisor in accordance with s. 122 (2) (b). Upon a consideration of the evidence my brother Walsh accepted ICI's estimate but in my opinion it is unnecessary to consider whether that estimate was correct. I hold that upon the proper construction of the section it is left to the taxpayer to make his own estimate of the life of the mine and (unless, perhaps, that estimate is not a genuine one) the Commissioner and the Court are bound to accept it. The scheme of div. 10 of Pt III of the Act, as in force at the relevant time, stated very broadly, was to permit a taxpayer to recoup all his capital expenditure of the kind referred to in s. 122 before paying tax on the profits from his mining operations. Under that division the taxpayer was given a variety of choices which, without going into full detail, may be summarized as follows. First, he could deduct a proportion of his residual capital expenditure in accordance with s. 122 (2). Since the residual capital expenditure was reduced by the amount of any deduction allowed under the section (s. 122 (5) (a)), if the estimate of the life of the mine made in one year was low, so that the amount of the deduction was proportionately high, the amount of deduction available in the following year would have been correspondingly reduced. Unless the taxpayer made an election to the contrary, the maximum amount of the deduction available under s. 122 was "an amount equal to so much of the assessable income of the year of income as remains after deducting all allowable deductions, other than deductions allowable under this section or under section one hundred and twenty-three aa " (sub-s. (3)). The purpose of this provision was apparently to ensure that a taxpayer who did not derive enough profit in the year of income and in the seven succeeding years to recoup the expenditure, would not be prevented by s. 80 from getting the full benefit of s. 122. However, under s. 122 (4) the taxpayer had the right to elect that sub-s. (3) should not apply; then if the deduction exceeded the income in a particular year the excess would be a loss carried forward in accordance with s. 80. Secondly, the taxpayer could elect that expenditure on plant or development should be a deduction from the assessable income of the year of income in which the expenditure was incurred: s. 122A. In the case of housing and welfare expenditure, the taxpayer could elect to deduct the expenditure over five years: s. 122AB. The deductions under ss. 122A and 122AB were alternative to those allowed under s. 122. Thirdly, the taxpayer could elect to have a deduction where he had appropriated income for expenditure of a capital nature on plant or development although the amount of income so appropriated had not been actually expended in the year of income: s. 122B. Finally, the taxpayer could elect to have no deduction under the Division in respect of plant: s. 123; he could then claim ordinary depreciation under s. 54. If a taxpayer adopted the primary method of claiming a deduction under s. 122 it became necessary that an estimate should be made of the life of the mine. The section does not say by whom the estimate is to be made. There is, however, no reason to assume that it was intended that it should be made by the Commissioner. The facts necessary to enable such an estimate to be made, such as the extent of the mineral deposit, and the intentions and ability of the taxpayer to work it, would not be known to the Commissioner and would go beyond what would ordinarily appear in a return of income. No doubt the Commissioner could obtain information under s. 264 but he would not have it in the first place, and to make an estimate he would in many cases require an amount of geological and financial detail disproportionate to the collateral question to be decided. Having regard to the facts that div. 10 left a number of wide choices to the taxpayer, and that a taxpayer was not required to supply with his assessment the mass of material necessary to enable an estimate of the life of the mine to be made, in my opinion it should be concluded that it was intended that the estimate should be made by the taxpayer. I need express no opinion as to what the position would be if it were shown that the estimate were not a genuine one, for example, if the number of years estimated appeared so unreasonable, having regard to the material available, that no one could honestly have reached such a result. The Commissioner argued in the present case that on the evidence the estimate of thirteen years was wrong, or alternatively that there was no evidence on which it should have been found to be correct. However, the evidence fell far short of establishing that the estimate made was not a genuine one. Whether, on the evidence, the estimate was right or wrong ICI was, in my opinion, entitled to take thirteen as a divisor for the purposes of s. 122 (2), since thirteen was the number of years in fact estimated as the life of the mine, and was of course a period less than twenty-five years.