16 In any event, there is a further obstacle to regarding the potential Trade Practices Act claim as one giving rise to a set off, which was adverted to by the Master. The concept of a set off was examined in some detail in Westwind Air v Hawker De Havilland (1990) 3 WAR 71, by Murray J, particularly at 84 - 85. The conclusions expressed by his Honour, which in my view are applicable to the present case, are as follows. At law it has always been the case that a claim for an unliquidated sum could not be set off against a liquidated claim. That is what the appellant seeks to do here. So far as equitable set off is concerned, a defendant could establish it only by bringing forward a claim which "impeaches" that of the plaintiff. It is not sufficient that there be countervailing claims, nor that the claims be mutual, nor even that they arise out of the same transaction. As I have noted, the conduct of which the appellant complains was conduct which arose long after the original loan agreements (in May 1999) and significantly after the date of the April 2001 deeds upon which the respondent now sues. It is "connected" or bound up with those agreements only to the extent that the existence of the obligation to repay appears to have been a factor upon which it is alleged that persons connected with the respondent relied in pressing the appellant to act in a particular manner. In my view no equitable set off can arise in those circumstances. It appears to me that the civil conspiracy claim is also incapable of giving rise to any set off, and for the same reasons.