Special Drawing Rights (SDR), are often referred to as the IMF's currency founded in 1969. Although that is useful shorthand, the SDR is not, in fact, a currency, but rather the IMF's unit of account. It is a measure of a country's reserve assets in the international monetary system. The value of an SDR is defined as the value of a fixed amount of yen, dollars, pounds and euros, expressed in dollars at the current exchange rate. The composition of the basket is altered every five years to reflect changes in the importance of different currencies in the world's trading system.