" Shorn of the parts with which we are not concerned, the rule provides that in any case in which the Income tax Officer is of the opinion that the actual amount of income, profits or gains accruing or arising to any person residing out of the taxa ble territories, whether directly or indirectly, through or from any business connection in the taxable territories cannot be ascertained, the amount of such income, profits or gains for the purpose of assessment to income tax may be calcu lated (i) on such percentage of the turnover so accruing or arising as the Income tax Officer may consider to be reasonable, or (ii) on an amount which bears the same propor tion to the total profits of the business of such person (such 212 profits being computed in accordance with the provisions of the Indian Income tax Act) as the receipts so accruing or arising bear to the total receipts of the business, or (iii) in such other manner as the Income tax Officer may deem suitable.