A method for calculating the correct value of a currency, which may differ from its current market value. It is helpful when comparing living standards in different countries, as it indicates the appropriate exchange rate to use when expressing incomes and prices in different countries in a common currency. By correct value, economists mean the exchange rate that would bring demand and supply of a currency into equilibrium over the long-term. The current market rate is only a short-run equilibrium. Purchasing power parity (PPP) says that goods and services should cost the same in all countries when measured in a common currency. PPP is the exchange rate that equates the price of a basket of identical traded goods and services in two countries. PPP is often very different from the current market exchange rate. Some economists argue that once the exchange rate is pushed away from its PPP, trade and financial flows in and out of a country can move into disequilibrium, resulting in potentially substantial trade and current account deficits or surpluses. Because it is not just traded goods that are affected, some economists argue that PPP is too narrow a measure for judging a currency’s true value. They prefer the fundamental equilibrium exchange rate (FEER), which is the rate consistent with a country achieving an overall balance with the outside world, including both traded goods and services and capital flows. (See Big Mac index. )