Purchasing power
Purchasing power parity is an economic term for measuring prices at different locations. It is based on the law of one price, which says that, if there are no transaction costs nor trade barriers for a particular good, then the price for that good should be the same at every location. Ideally, a computer in New York and in Hong Kong should have the same price. If its price is 500 US dollars in New York and the same computer costs 2000 HK dollars in Hong Kong, PPP theory says the exchange rate should be 4 HK dollars for every 1 US dollar.