In practice, in the unique linked exchange rate system, the exchange rate of HK$7.80 = US$1, is strictly controlled by the Hong Kong Monetary Authority in the foreign exchange market by controlling supply and demand of Hong Kong dollars in order to influence the exchange rate being fixed. By this arrangement the HKMA guarantees to exchange United States dollar into Hong Kong dollars and vice versa, at the rate of 7.80. When the market rate is below 7.80, the banks will convert United States dollar for Hong Kong dollars from the HKMA, Hong Kong dollars supply will increase, and the market rate will climb back to 7.80.