When tax is calculated in a foreign currency, the exchange rate used is the rate effective on the date of the corresponding document. This may differ from the rate that is effective on the tax date. For example, during invoice post, the exchange rate used for tax, if applicable, is the same as the rate used for the rest of the invoice; however, it may be different from the rate that was in effect during shipment. Based on local regulations, it may be necessary to reevaluate using the official exchange rate.