The third aspect of the SFAC 6 definition is that future sacrifices are a result of past transactions or events. While depreciation is described as an internal event (FASB, 1992, par. 138), temporary differences between taxable income and financial statement income are not caused by the event of depreciation. The differences occur because of the use of alternative methods of depreciation. Since the law allows alternative allocation schemes, the resulting taxable income and accounting income are caused by different allocation methods and estimates of residual value. They are not the result of past transaction or events since estimates of useful life and residual values must reflect future usefulness. In addition, if the Federal government lowers the tax rate, deferred tax balances are reduced.