7. Where a deficiency of profits occurs in any chargeable accounting period in any business, the profits of the business chargeable with excess profits tax shall be deemed to be reduced and relief shall be granted in accordance with the following provisions:- (a) the aggregate amount of the profits so chargeable for the previous chargeable accounting periods shall be deemed to be reduced by the amount of the deficiency of profits and the amount of excess profits tax payable in respect thereof shall be deemed to be reduced accordingly and the relief necessary to give effect to the reduction shall be given by repayment or otherwise; (b) where the amount of the deficiency of profits exceeds the aggregate amount of the profits so chargeable for the previous chargeable accounting periods, or where there is no previous chargeable accounting period, the balance of the deficiency of profits or the whole of the deficiency, as the case may be, shall be applied in reducing any profits so chargeable for the next subsequent chargeable accounting period, and if and so far as it exceeds the amount of those profits, any profits so chargeable for the next subsequent chargeable accounting period and so on: Provided that a deficiency of profits occurring in a chargeable accounting period beginning on or after the 1st day of April, 1941, shall first be applied so as to reduce profits chargeable to tax arising in another chargeable accounting period beginning on or after the said 1st day of April, and a deficiency of profits occurring in a chargeable accounting period ending on or before the 31st day of March, 1941, shall first be applied so as to reduce profits chargeable to tax arising in another chargeable accounting period ending on or before the said 31st day of March; and where owing to an insufficiency of profits for chargeable accounting periods ending on or before the said 31st day of March, or, as the case may be, beginning on or after the said 1st day of April, the whole or any part of the deficiency is applied otherwise than as aforesaid- (a) the application shall be treated as provisional only; and (b) if it thereafter appears that there is no longer such an insufficiency as aforesaid, such adjustment shall be made as the National Board of Revenue may by written order direct: Provided further that where a chargeable accounting period falls partly before and partly after the end of March, 1941, the provisions of the preceding proviso shall apply as if so much of the chargeable accounting period as falls before, and so much of the chargeable accounting period as falls after, the said end of March, were each a separate chargeable accounting period, and as if the deficiency of profits of that separate chargeable accounting period were an apportioned part of the deficiency of profits occurring in the whole period; and any apportionment required to be made by this proviso shall be made by reference to the number of months or fractions of months in each of the parts of the whole chargeable accounting period.