Due to the variety of foreign currencies, countries usually choose one currency as the key currency when setting their own exchange rates. First, they set the exchange rate of their own currency against this currency, which is called the benchmark exchange rate. Then calculate the exchange rate of local currency against other currencies according to the set benchmark exchange rate. Key currency generally refers to the most commonly used world currency in domestic and foreign economic exchanges. Widely used in pricing, settlement and reserve currency, freely convertible and internationally accepted. At present, the key currency is usually the US dollar, with the exchange rate of the domestic currency against the US dollar as the benchmark exchange rate.
The exchange rates of other foreign currencies and domestic currencies can be calculated according to the exchange rates and benchmark exchange rates of this currency and major currencies in the international market. Calculating exchange rate is calculating exchange rate, also known as cross exchange rate.