The Federal Circuit Cienega X decision imposes insufficient financial analysis of Penn Central’s two economic prongs to satisfy either economic practice or the Penn Central test. The decision’s imposed change in value measurement evaluates only one prong of the Penn Central test. Change in value satisfies the economic impact prong but does not establish severity of the economic impact vis-à-vis frustration of distinct investment-backed expectations (DIBE). Mere diminution is well-known to be inadequate to reveal whether economic viability has been destroyed by the regulatory prohibition. This must be determined with reference to the second economic prong of Penn Central—frustration of DIBE, a simple and definitive financial calculation. Progeny of Cienega X discussed in this Article do not include a complete analysis of the three-pronged Penn Central test.