Has the meaning given to that term in BC1 of the Grid Code. Calculated as the difference between the sum of all Physical Notifications for exporting BM Units (i.e. the Indicated Generation) and the Demand Forecast. Data supplied by the System Operator for the day ahead and current day (a number of times each day) for publication on the BMRS, comprising the Indicated Imbalance for each System Zone and the national value for each Settlement Period.