The economic limit is defined as the time (date) when the maximum cumulative net cash flow occurs for a project.  Operating costs should include only those costs that are incremental to the project for which the economic limit is being calculated (i.e., only those cash costs that will actually be eliminated if project production ceases).  The economic limit, should exclude depreciation, ADR (Abandonment, Decommissioning and Reclamation) costs, and income tax as well as any overhead that is not required to operate the subject property.  For a given project, no future development costs can exist beyond the economic limit date.  Interim negative project net cash flows may be accommodated in periods of development capital spending, low product prices, or major operational problems provided that the longer-term cumulative net-cash-flow forecast determined from the effective date becomes positive.