During the era of state control (1924-91), the Mongolian tughrik had a fixed rate (4 to the U.S. dollar in 1989), and was not freely convertible. With the introduction of convertibility in the early 1990s, there was a sudden surge in hard currency demand and the tughrik depreciated (dropped in value) sharply (MT448.61 to the U.S. dollar in 1995 and MT1,072.37 to the U.S. dollar in 1999). The Mongolian government has tried to stabilize its currency and its economy by relying heavily on international assistance from the World Bank and the IMF. The annual rate of inflation , which soared to around 300 percent in 1993, was reduced to 15 percent in 2000. The Bank of Mongolia, the nation's central bank, seeks to maintain a tight monetary policy in order to stabilize the value of the currency and reduce inflation.