Hi Barb,

Yes, it is definitely possible to add horizontal error bars in Excel 2007. Here's how you can do it:

1. First, select the data series to which you want to add the horizontal error bars.
2. Next, click on the "Layout" tab in the ribbon at the top of the screen.
3. In the "Analysis" group, click on the "Error Bars" button and select "More Error Bar Options" from the dropdown menu.
4. In the "Format Error Bars" dialog box that appears, click on the "Error Bars" tab.
5. Under "Error Amount," select the "Custom" option and click on the "Specify Value" button.
6. In the "Custom Error Bars" dialog box, click on the "Custom" option under "Error Amount."
7. Now, you can enter the values for your horizontal error bars. You can either enter a constant value, or you can select a range of cells that contain the values you want to use.
8. Once you have entered your values, click "OK" to close the dialog boxes.

Your horizontal error bars should now be visible on your chart. If you need to make any adjustments, you can always go back to the "Format Error Bars" dialog box and make changes as needed.