The law of income tax in a modern society is intended to achieve various social and economic objectives. It is often used as an instrument for accelerating economic grnwth and development. Section 1 SC is a provision intrnduced in the Indian Income Tax Act, 1922 with a view to carrying out this objective and it is calculated to encourage setting up of new industri~l undertakings in the country. Sub-section (I) of this section exempts from tax so much of the profits or gains derived from a new industrial undertaking as do not exceed 6% per annum of the capital employed in the undertaking. There are rules made under the Act for computing the capital employed in a new industrial undertaking but we are not concerned with these rules in the present appeals. What is material is only the provision for exemption and according to this provision, the profits and gains of a new industrial undertaking are exempt from tax to the extent of 6% per annum of the capital employed, and obviously, therefore, there must be prnfits or gains derived from the new industrial undertaking in the assessment year in question before any claim for exemption can be sustained under section 15 C, sub-section (1 ) . If there are no profit or gains derived from the new industrial undertaking in any particular assessment year, there can be no question of any exemption, because it is only where there are such profits or gains that to the extent of 6% per annum of the capital employed, they become eligible for exemption. The first question which must, therefore, arise for consideration in every case where a claim for exemption is made under section !SC, sub-section(!) is whether there are any profits or gains derived from the new industrial undertaking in the assessment year in question, and if so, what is the quantum of such profits or gains. Now, sub-section (3) of section 15C says that the profits or gains of a new industrial undertaking shall be computed in accordance with the provisions of section 10 and since under the income tax law, every assessment year is a self-contained period, prnfits and gains of the new undertaking must be computed for the particular assessment year in respect of which the claim for exemption is made, by applying the provisions of section 10. Sub-section (2) of that section provides for various allowances to be made in computing profits and gains of a business and amongst such allowances are one in respect of depreciation and the other in respect of development rebate. Gause (vi) of sub-section '(2) deals with allowance for depreciation and it says that in computing the profits or gains of a business allowance shall be made, in respect of depreciation of building, machinery, plant or furniture belonging to the assessee and used for the purpose of the business, a sum equivalent to "such percentage on the written down value thereof as may in any case or class of cases be prescribed". Depreciation cal-