If you want the position of the interface on a vertical line you can: 1. Create the vertical line 2. Create a point with the method ‘Variable Maximum’, location ‘Line 1’, variable ‘Water.Conservative Volume Fraction.Gradient’ 3. Create an expression ZInterfaceLine1 = probe(Z)@Point 1 4. Create a chart of type ‘Time’ and for Chart Line choose the method ‘expression’ and set ZInterfaceLine1 in the expression box. Note that to do this, you will need to have stored the Conservative Volume Fraction Gradient in the trn files. To get the average position of the interface with time, you can: 1. Create an isosurface at the fluid volume fraction of 0.5 2. Create an expression like AverageZInterface = areaAve(Z )@Isosurface 1 3. Create a chart of type ‘Time’ and for the Chart Line choose the method ‘expression’ and set AverageZInterface in the expression box.