means the lowest price, on the date of the transaction or other manner of acquisition of a listed security, at which that security was traded on the exchange on which it is listed, as determined by that exchange on each day on which trade in that security occurs on that exchange: Provided that where that security was not traded on the date of the transaction or other manner of acquisition, the lowest price of that security must be regarded as being the lowest rice on the last business day, preceding the date of the transaction or other manner of acquisition, on which that security was traded on that exchange;