Reserve currency before the beginning of the worldwide credit crunch related recession and Eurozone crisis, which harmed the euro and slowed its adoption. Since 2009, the reserve currency use of the euro has continued to drop, down to 23.9 percent in 2013. The Dutch guilder was the "de facto" reserve currency in Europe in 17th and 18th centuries. The United Kingdom's pound sterling was the primary reserve currency of much of the world in the 19th century and first half of the 20th century. The emergence of the USA as an economic superpower, and the establishment of the U.S. Federal Reserve System
WCU – World Currency Unit base years are spliced to form a continuous series. The formula for the valuation of the World Currency Unit has been revised since 2008 so that the GDP weights are now revised every year. While still retaining the meaning of a unit of global real purchasing power, the WCU can now be interpreted as a GDP-weighted basket of currencies, each indexed against domestic inflation. The GDP-weighted basket of currencies has now formed the basis for a new formula for the effective exchange rate. The nominal value of this unit would rise with inflation in each economy. Moreover, the nominal value