As the purpose is to determine a rate that best preserves the purchasing power of the 18 per cent dollar component of the current budget, the duration of the averaging period should, in theory, fully coincide with the current biennium.
由于目的是确定最能保持现行预算中18％的美元部分的购买力，因此，从理论上讲，计算平均汇率的期间应完全等同于现两年期。