Basically, the foreign exchange market together with general economic principles. Thus, the market moves is a request(demand)and supply(supply).Well, supply and demand was triggered by a variety of economic data is in a state that what happened to the economy of a country, would lead to currency movements (can be) very large. In addition, currency movements in the foreign exchange market is also often occurs due to trade between countries in the process of purchasing selling. In fact, if you use credit cards overseas, it just means you're doing foreign exchange transactions because every transaction you make with the concerned country's currency, will be converted into rupiah currency to billing your credit card bills.
