The Commissioner does not dispute that the cost of the discount, converted to Australian dollars, is a loss or outgoing of the taxpayer "incurred in carrying on a business for the purpose of gaining or producing income" and is an allowable deduction for the purposes of s 51 of the Income Tax Assessment Act 1936 Cth (the Act). However, he contends that the cost of the discount is to be calculated by deducting the proceeds of the notes, converted into Australian dollars at the issue date, from the cost of discharging the notes, converted into Australian dollars at the maturity date of the notes. Alternatively, the Commissioner claims that the cost of the discount is to be calculated by converting the discount into Australian dollars at the maturity date and deducting from it the reduced value of the proceeds of the issue at the maturity date. The taxpayer, on the other hand, contends that it did not incur any loss or outgoing for the purpose of s 51 until the maturity date of the notes and that, for the purpose of s 51, that loss is the Australian dollar equivalent at that time of the cost of the discount expressed in US dollars. Because the Australian dollar generally appreciated in relation to the US dollar during the relevant periods, the allowable deduction would be less under the Commissioner's methods than under the taxpayer's method. Indeed, for some transactions, the Commissioner's methods would produce the result that the discount cost was "negative". The question in this appeal is which, if any, of these methods is the correct method for calculating the loss or outgoing admittedly incurred by the taxpayer.