Non-performance is failure by a party to perform any of its obligations under the contract, including defective performance or late performance. The aggrieved party is entitled to full compensation for harm sustained as a result of the non-performance. Such harm includes both any loss which it suffered and any gain of which it was deprived, taking into account any gain to the aggrieved party resulting from its avoidance of cost or harm. Such harm may be non-pecuniary and includes, for instance, physical suffering or emotional distress. Damages are to be paid in a lump sum. However, they may be payable in instalments where the nature of the harm makes this appropriate. Damages to be paid in instalments may be indexed. Damages are to be assessed either in the currency in which the monetary obligation was expressed or in the currency in which the harm was suffered, whichever is more appropriate. If a party does not pay a sum of money when it falls due the aggrieved party is entitled to interest upon that sum from the time when payment is due to the time of payment whether or not the non-payment is excused.