In some jurisdictions, a utility plant must be considered both prudent and used and useful before being allowed into the rate base (1,4). Prudent means the investment is reasonable based on cost-minimizing criteria. There are two perspectives. In one view, the investment is considered prudent if it was prudent at the time the decision was made. This requires accurately assessing what information management had available and used to make its decision. In the second perspective, the investment is prudent if management acted to minimize costs by fully considering changing conditions that would affect the investment. This requires assessing what management should have known and should have considered in making its decision.