7 Secondly, even if there had been a ground of appeal contending that the judge erred in failing to find that the alleged tortious claim constituted an equitable set-off, there was no adequate evidence of the likely quantum of the appellant's claim. In seeking to resist an application for summary judgment based on an equitable set-off, the defendant must not only establish that it has an arguable claim on breach, but must also put before the court sufficient evidence to enable the court to make some assessment of the likely quantum of the defendant's claim. A defendant will not, in seeking to resist a summary judgment application, establish an arguable defence of set-off if the evidence in support of the quantum of its claim is so vague, uncertain and lacking in substance, that the court is unable to make any informed assessment of its likely quantum and whether the quantum is likely to reach or exceed the level of the plaintiff's claim in debt: Melbourne Glass Pty Ltd v Coby Constructions Pty Ltd (1997) 14 BCL 409, 418 - 419. The appellant's affidavit evidence before the judge was that the appellant had lost revenue from the respondent supplying the units directly to the mining company after the respondent had terminated its contract with the appellant. However, the claim for revenue, without deducting expenses, gave no indication of the likely quantum of the appellant's loss. A somewhat desultory attempt was made by counsel for the appellant, at the hearing of the appeal, to work out what the appellant's loss may have been. It transpired that whatever the figure might be, it would probably be nowhere near the level where it could be thought to impeach the whole of the respondent's claim in debt. In any event, it was apparent that counsel had no real confidence in his calculations, and that they could not be used to justify the orders sought by the appellant in the appeal.