The Exchange Rate Mechanism was a system introduced by the then European Community in 1979 as part of the European Monetary System (EMS) which was designed to reduce exchange rate fluctuations in preparation for Economic and Monetary Union (EMU) and the eventual introduction of the EU's single currency, the euro. Currencies were allowed to fluctuate no more than 2.25 percent above or below fixed bilateral rates. The United Kingdom joined in 1990 but was forced to leave in 1992 when sterling came under speculative pressure. Fluctuation bands were widened to plus or minus 15 percent in 1993. The ERM has been superseded by a new system known as ERM II which EU countries wishing to adopt the euro are required to join for two years prior to euro zone membership. Their currencies are confined within a set rate against the euro of plus or minus 15 percent.