Prior to April 1, 1968, section 33(1)(iii)(c)(A) of the Income Tax Act, 1961 provided: "(1) In respect of a new ship acquired or new machinery or plant (other than office appliances or road transport vehicles) installed after the 31st day of March, 1954, which is owned by the assessee and is wholly used for the purposes of the business carried on by him, a sum by way of development rebate, equivalent to (i) . . . . . . . . (ii) . . . . . . . . (iii) in the case of machinery or plant installed after the 31st day of March, 1961 (a) . . . . . . . . (b) . . . . . . . . (c) where the machinery or plant is installed after the 31st day of March, 1965 (A) for the purposes of business of construction, manufacture or production of any one or more of the articles or things specified in the list in the Fifth Schedule (a) thirty five per cent, of the actual cost of the machinery or plant to the assesee, where it is installed before the 1st day of April, 1970.