C1FlexChart enables users to show a line marker in the chart area that displays precise data values for a specific point or position. The Line Marker draws horizontal or vertical lines over the plot area with relative data values displayed near by. Users can set these lines as static or interactive by using Interaction method. To customize the direction in which the line marker displays the data values, use the Alignment method and set it to LineMarkerAlignment.Auto. You can also set the orientation of the lines using Lines method.

The following image shows an interactive line marker aligned at Auto position and its line set to Vertical position.

The code given below illustrates how to set the Line Marker feature. 

//setting the Line Marker
mChart.Marker.Visible = true;
mChart.Marker.Interaction = ChartMarkerInteraction.Drag;
mChart.Marker.Alignment = ChartMarkerAlignment.Auto;
mChart.Marker.VerticalPosition = 1d;
mChart.Marker.Lines = ChartMarkerLines.Vertical;