I have an XY scatter chart showing the relationship between % organic and the retention time of compounds on an HPLC. I have the user select a given % organic on the X axis. I would like to display a vertical line on the chart at the selected % organic on the X axis. I can scale the Y axis to the min/max of the values. So how can I do a combo chart or whatever, to overlay a vertical line to the scale of the chart, at the X axis selected % organic?