P bought defective turbines from D and for a while used them, before purchasing ones of a superior quality, and which would have been of a superior quality, even if the defective turbines had worked. P then sued for the extra petrol that the bad turbines had consumed while in use AND the whole cost of replacing them. HL ruled that the extra benefit gained from having superior quality turbines had to be taken into account in assessing the damages since this extra benefit (and cost of acquiring it) had nothing to do with the original contract. Where P took steps naturally arising from the breach, as here, it is necessary to look at any additional benefits which he thereby acquired and to "balance loss and gain.”- Viscount Haldane. He also states that in accordance with the principle that P is supposed to be placed in as good a situation as if the contract had been performed, the aim is to reverse the pecuniary loss flowing from the breach and discount any incidental benefits. The plaintiff has a “duty of taking all reasonable steps to mitigate the loss consequent on the breach,” and failure to do so will reduce the amount recoverable by the plaintiff.