A target, or goal line, is an imaginary horizontal line on a chart that represents a certain level of performance. For example, in a chart for academic performance, the target line might be set at the typically passing grade of 70 per cent. The target lines gives a viewer a quick visual way to see how many items on the chart are underperforming and how many are over-performing. While Excel doesn't have a menu option to add a horizontal line, you can make a horizontal line on your chart by adding a dummy series.
Locate the chart data on your Excel worksheet. If you aren't sure which data was used for the chart, click once on the chart: the chart data will be bordered by a blue line on the worksheet.
Click on the first blank cell to the right of your chart data. If you don't have a blank column directly to the right of your chart data, create one: right click, then click "Insert" and then click "Entire column."
Type your target. For example, if your graph consists of sales figures and your target sales goal is 20 units, type "20."
Click the fill handle for the cell. The cell looks like a little black square at the bottom right of the cell. Drag it down the column to the last row in your chart data. This action copies the input for the cell (in this example, 20) to all cells in the column. This is the dummy series for your chart.
Highlight the entire chart data area, including the dummy series. To highlight the data, left click at the top left of the cells and then drag the cursor to the bottom right.
Click the "Insert" tab. Select the chart type you want displayed. For example, click "Column" and then click "2D." Excel will insert the chart into the spreadsheet.
Click the dummy series on the chart, then click "Change Chart Type." Change the chart type to "Line."
If it's inconvenient to add an entire column to the right of your data, copy your chart data to the very bottom of your spreadsheet before adding the dummy data.