The gains chargeable to tax shall, subject to other provisions of this Act, be computed as follows —
(a)
in the case of a disposal of an asset used for a trade, business, profession or vocation, for which capital allowance has been made in accordance with the First Schedule to this Act, only the residue of that asset shall be deducted from the disposal proceeds for the purposes of computing chargeable gains ; and
(b)
where capital allowance has not been made in accordance with the First Schedule to this Act, the chargeable gain shall be determined by deducting from the disposal proceeds, the amount or value of the consideration, in money or money's worth incurred, wholly and exclusively for the acquisition of the asset.