Development rebate. — The deduction to be allowed by way of development rebate in respect of any ship or machinery or plant referred to in sub-section (1A) of section 33 shall be a sum equivalent to—

[(a) in the case of any such ship—(i) where the ship is acquired by the assessee at any time before the expiry of seven years from the date she was built, thirty per cent of the actual cost of the ship to the assessee ; and(ii) in any other case, twenty per cent of the actual cost of the ship to the assessee ;](b) in the case of any such machinery or plant installed after the 31st day of March, 1964—(i) where it is installed before the 1st day of April, 1966, for the purposes of business of mining coal, twenty per cent of the actual cost of the machinery or plant to the assessee ; and(ii) in any other case, ten per cent of the actual cost of the machinery or plant to the assessee.Explanation : In this rule, “actual cost” shall have the meaning assigned to it in clause (1) of section 43.