The contract provided, inter alia, for the payment of monthly instalments of £8 13s. 4d. "until the whole of the balance of the purchase money and all additions thereto shall be paid to the vendor, provided that if any sum shall remain owing or unpaid at the expiration of ten years from the date of this contract such sum shall thereupon immediately become due and payable ". The LESLIE.
additions referred to consisted of stamp duty, interest, rates, taxes, costs &. The purchaser undertook by cl. 21, in addition to the payments mentioned above, to pay on 1st May in each year a sum of not less than £50, and agreed that "the whole of the purchase moneys, interest, additions and accretions shall be paid not later than 1st February 1957. In the event of default in the payment of a monthly instalment of £8 13s. 4d. for a period of one hundred and eight days after the due date for the payment thereof the contract provided that "the whole of the balance of purchase money and all additions thereto shall at the option of the vendor be deemed to fall due and become immediately payable and the vendor shall be at liberty to sue the purchaser for the whole amount of the said balance of purchase money and all additions thereto".
After payment of a certain number of monthly instalments of £8 13s. 4d. each, the last such payment being made on 10th Novem- ber 1947, and of annual amounts, the last such payment being of the sum of £25 on 11th May 1950, the purchaser made default, whereupon the vendor exercised its option to deem the balance of the purchase money and the additions thereto as due and immediately payable. The total payments made by the purchaser under the contract, including the deposit of £100, amounted to the sum of £495 13s. 4d.
The balance claimed by the plaintiff-vendor to be due and payable was the sum of £4,112 10s. 4d., which sum he claimed was ascertained by the application of cll. 22 and 23 of the contract, which were in the following terms:-"22 Provided always and notwithstanding anything contained in this Contract it is hereby agreed by and between the parties hereto in order to provide for the equitable performance of this Contract in the event of inflation and/or deflation of price levels that if the Retail Price Index Number 'C' series (weighted average for all items of household expenditure for the six capital cities) published in the Common- wealth Statistician's Quarterly Summary of Australian Statistics (hereinafter called the Index Number) shall have increased by twenty-five per cent. or more above or decreased by twenty-five per cent. or more below the Index Number for the years 1923-