The balance of payments is a function of three components: transactions involving export or import of goods and services form the current account, transactions involving purchase or sale of financial assets form the financial account, and transactions involving unconventional transfers of wealth form the capital account. The current account summarizes three variables: the trade balance, net factor income from abroad, and net unilateral transfers. The financial account summarizes the value of exports versus imports of assets, and the capital account summarizes the value of asset transfers received net of transfers given. The capital account also includes the official reserve account, which summarizes central banks' purchases and sales of domestic currency, foreign exchange, gold, and SDRs for purposes of maintaining or utilizing bank reserves. Because the balance of payments sums to zero, a current account surplus indicates a deficit in the asset accounts and vice versa. A current account surplus or deficit indicates the extent to which a country is relying on foreign capital to finance its consumption and investments, and whether it is living beyond its means. For example, assuming a capital account balance of zero (thus no asset transfers available for financing), a current account deficit of £1 billion implies a financial account surplus (or net asset exports) of £1 billion. A net exporter of financial assets is known as a borrower, exchanging future payments for current consumption. Further, a net export of financial assets indicates growth in a country's debt. From this perspective, the balance of payments links a nation's income to its spending by indicating the degree to which current account imbalances are financed with domestic or foreign financial capital, which illuminates how a nation's wealth is shaped over time. A healthy balance of payments position is important for economic growth. If countries experiencing a growth in demand have trouble sustaining a healthy balance of payments, demand can slow, leading to: unused or excess supply, discouraged foreign investment, and less attractive exports which can further reinforce a negative cycle that intensifies payments imbalances. A country's external wealth is measured by the value of its foreign assets net of its foreign liabilities. A current account surplus (and corresponding financial account deficit) indicates an increase in external wealth while a deficit indicates a decrease. Aside from current account indications of whether a country is a net buyer or net seller of assets, shifts in a nation's external wealth are influenced by capital gains and capital losses on foreign investments. Having positive external wealth means a country is a net lender (or creditor) in the world economy, while negative external wealth indicates a net borrower (or debtor). Nations and international businesses face an array of financial risks unique to foreign investment activity.