No city ought to consider its budget truly balanced unless it reduces revenues by the costs of physical depreciation and provides for reserves to cover it.

One - supposing that it is one year's cost that is to be considered - is to sell it, earn interest on the owner's capital thus released, and buy it back a year later, making an allowance for its physical depreciation.

In economics, depreciation is the gradual decrease in the economic value of the capital stock of a firm, nation or other entity, either through physical depreciation, obsolescence or changes in the demand for the services of the capital in question.