(2)Such profits or gains shall be computed after making the following allowances, namely (vi)in respect of depreciation of such buildings, machinery, plant or furniture being the property of the assessee, a sum equivalent, where the assets are ships 765 other than ships ordinarily plying on inland waters, to such percentage on the original cost thereof to the assessee as may in any case or class of cases be prescribed and in any other case, to such percentage on the written down value thereof as may in any case or class of cases be prescribed : and where the buildings have been newly erected, of the machinery or plant being new, not being machinery or plant entitled to the development rebate under, clause (vi b), has been installed, after the 31st day of March, 1945, a further sum (which shall however not be deductible in determining the written down value for the purposes of this clause) in respect of the year of erection or installation equivalent (a) in the case of buildings the erection of which is begun and completed between the 1st day of April 1946 and the 31st day of March 1956 (both days inclusive), to fifteen per cent of the cost thereof to the assessee; (b) in the case of other buildings, to ten per cent of the cost thereof to the.