The fluctuation of exchange rates has given rise to problems of allocating the advantage or disadvantage resulting from changes in exchange rates. In one situation, the problem is bilateral, arising between the parties to a transaction or series of transactions. In the case of disagreement between them on the appropriate exchange rate for settlement when there are two or more possible rates, the advantage that one party enjoys because of the rate that is chosen is matched by the correlative disadvantage suffered by the other party. This kind of problem arises in many forms between the parties to a contract. Sometimes, the judicial solution of a problem may depend on interpretation of the contract.1 In other cases, the outcome may depend on the interpretation of an international convention,2 or the way in which a particular legal concept, such as restitutio in integrum, is applied.3 In some cases, courts have relied on the proposition that a party should have taken steps to protect itself against exchange risk in accordance with the normal practice of the trade in which the transaction or transactions occur.4 It may even be possible to imply a term that a party is to behave in this way.