One of the major responsibilities of Southeastern is to design, formulate, and justify rate schedules. Repayment studies prepared by the agency determine revenue requirements and appropriate rate levels and these studies for each of Southeastern's four power marketing systems are updated annually. They demonstrate the adequacy of the rates for each system. Rates are considered to be adequate when revenues are sufficient to repay all costs associated with power production and transmission costs, which include the amortization of the Federal investment allocated to power.