The Import and export constraint limits for a BMRS Zone. The Import constraint limit being calculated as the boundary transfer limit minus the Demand Forecast plus the sum of Maximum Export Limits for exporting BM Units and the export constraint limit being calculated as the boundary transfer limit plus the Demand Forecast minus the sum of Maximum Export Limits for exporting BM Units. 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 Constraint Boundary Margin for each System Zone and the national value for each Settlement Period.