The global financial crisis of 2008 exposed the fact that risk-based capital adequacy doesn't capture potential future losses comprehensively. As a result, Basel III introduced a minimum leverage ratio that is designed to be an additional backstop to the capital requirements. The leverage ratio is designed to limit the amount of leverage a bank can take and is calculated by dividing the bank's tier 1 capital by their total exposure. Simply put, the total exposure metric is usually measured as total assets on the balance sheet, but this can be extended to include off balance sheet exposures and national regulators have taken slightly different routes in specifying how this is calculated. This is the case for the supplementary leverage ratio or SLR imposed by the Federal Reserve on US Banks. The SLR's Denominator total leverage exposure includes balance sheet and some off balance sheet items. In the UK version, the UK leverage ratio, the leverage exposure measure excludes cash held at central banks, but otherwise is the total value of assets on a bank's balance sheet. A low leverage ratio indicates relatively small amounts of capital relative to the assets a bank holds increasing the risk of financial distress should the value of those assets fall by a greater than expected amount. The minimum leverage ratio as stipulated within Basel III is that the ratio must not fall below 3%. However, as larger banks measured by the size of their balance sheet pose a larger risk to the economy, should they fail, they have more stringent leverage ratio minimums. Basel III stipulates a minimum 5% leverage ratio for globally systemically important banks. However, national regulators can adapt this to suit their needs. For example, the Prudential Regulation Authority in the UK has a minimum ratio of 3.25%, but includes additional buffers for size and additional counter-cyclical risks.