(a)[ for the purposes of acquiring, before the expiry of a period of ten years next following the previous year in which the ship or aircraft was acquired or the machinery or plant was installed, a new ship or a new aircraft or new machinery or plant [other than machinery or plant of the nature referred to in clauses (a), (b) and (d) of ] [Inserted by Act 66 of 1976, Section 8 (w.e.f. 1.4.1976).][the second proviso to sub-section (1)] [ Substituted by Act 3 of 1989, Section 6, for " the proviso" (w.e.f. 1.4.1989).][for the purposes of the business of the undertaking; and [Inserted by Act 66 of 1976, Section 8 (w.e.f. 1.4.1976).]