(4)In making any such provisional assessment the Income- tax Officer shall make allowance for any deficiencies of profits for previous chargeable accounting periods which are under the provisions of section 6 to be set off against the taxable profits of the chargeable accounting period in respect of which the assessment is being made: Provided that, where such deficiencies of profits have not been determined under sub- section (1) of section 12, the Income- tax Officer shall estimate the amount thereof to the best of his judgement.
