the exchange rate has often been problematic as the markets often want the currency to move in the opposite direction to governments. Developing countries in particular would often experience difficulties, though even advanced economies like Britain had issues, with Black Wednesday an example when she had insufficient reserves to counter the market.</ref> in a rules based or managed currency regime, and when left to float freely in the market they also tend to change in the direction that will restore balance. When a country is selling more than it imports, the demand for its currency will tend to increase as other countries ultimately need the selling country's currency to make payments for the exports. The extra demand tends to cause a rise of the currency's price relative to others. When a country is importing more than it exports, the supply of its own currency on the international market tends to increase as it tries to exchange it for foreign currency to pay for its imports, and this extra supply tends to cause the price to fall. BoP effects are not the only market influence on exchange rates however, they are also influenced by differences in national interest rates and by speculation. Rebalancing by adjusting internal prices and demand When exchange rates are fixed by a rigid gold standard, or when imbalances exist between members of a currency union such as the Eurozone, the standard approach to correct imbalances is by making changes to the domestic economy. To a large degree, the change is optional for the surplus country, but compulsory for the deficit country. In the case of a gold standard, the mechanism is largely automatic. When a country has a favourable trade balance, as a consequence of selling more than it buys it will experience a net inflow of gold. The natural effect of this will be to increase the money supply, which leads to inflation and an increase in prices, which then tends to make its goods less competitive and so will decrease its trade surplus. However the nation has the option of taking the gold out of economy (sterilising the inflationary effect) thus building up a hoard of gold and retaining its favourable balance of payments. On the other hand, if a country has an adverse BoP it will experience a net loss of gold, which will automatically have a deflationary effect, unless it chooses to leave