Hi Rich,

Currently there is no build-in funticonality to draw a target line. You can try with the Marks on the Axis but I'm not sure it would works in your scenario.

<igCA:XamChart.Axes>
            <igCA:Axis AxisType="PrimaryY">
                    <igCA:Axis.MinorGridline>
                              <igCA:Mark Unit="60" Stroke="Red" StrokeThickness="3" />
                    </igCA:Axis.MinorGridline>
             </igCA:Axis>
</igCA:XamChart.Axes>

Alternately you can place the XamChart in a canvas and draw a line at the top.

In order to possibly get this feature into a future release, please submit a feature request at the following webpage:
http://devcenter.infragistics.com/Protected/RequestFeature.aspx

I hope this helps

Vlad