put a vertical line in the middle of the surface

Hi Abolfazl Ghanbari,

Did you try to use VerticalLineAnnotation with CoordinateMode = RelativeX?

        VerticalLineAnnotation verticalLine = sciChartBuilder.newVerticalLineAnnotation()
            .withX1(0.5)
            .withCoordinateMode(AnnotationCoordinateMode.RelativeX)
            // here goes the rest of annotation's configuration
            .build();

Hope this will help you!

Best regards,
Yura