This use case is a description of the information exchanges between a Data Acquisition subsystem and the load frequency control core of an Automatic Generation Control system. The calculation of economic dispatch and handling of generator schedules and production cost summaries form a separate use case [undocumented at present]. The AGC Load Frequency control subsystem receives new data values from the Data Acquisition subsystem (i.e. SCADA), calculates an Area Control Error and the required changes in generating unit set points. Set point controls are sent through the Data Acquisition subsystem to the power stations. The generating unit states can be made available for other applications. For simplicity, the information exchanges with user interfaces are not described. It can be assumed that user interfaces are notified with relevant data updates for each subsystem and provide a means of changing parameters.