The precursor to the euro. A composite, artificial currency based on a basket of EU member currencies weighted according to each country's share of EU output. The exchange rates between EU member currencies were based on each currency's value in Ecus. These arrangements were regulated through the European Monetary System (EMS). When a currency diverged too much from its central Ecu rate, the country concerned was forced to take action - a process called the Exchange Rate Mechanism (ERM).