Depreciation charges against income, based on book values, are very crude approximations of deterioration in the economic value of physical plant. The actual deterioration will not be known until the asset is retired or sold. And projections of future investment returns on defined-benefit pension plans markedly affect corporate pension contributions and, hence, pre-tax profits.
Thus, how one chooses to evaluate the future income potential of the balance sheet has a significant impact on current reported earnings. *  *  *  Earnings uncertainty has been particularly elevated in recent years.