The spline curve can be interactively modified by selecting and moving the spline nodes with the mouse. The user is free to delete or add more spline nodes, so that any desired curve characteristic can be achieved. The adjustment of the valve lift width is done with a central sampling point, which can be distinguished from the other spline nodes due to its red colour. If the user activates this central spline point, the width of the valve lift can be adjusted with respect to the cam shaft angle just by moving a slider bar.