To superimpose one chart onto another in Excel, you can follow these steps:

1. Select the chart that you want to add the other chart to.
2. Click on the "Design" tab in the ribbon at the top of the screen.
3. Click on the "Select Data" button in the "Data" group.
4. In the "Select Data Source" dialog box, click on the "Add" button under "Legend Entries (Series)".
5. In the "Edit Series" dialog box, enter a name for the new series in the "Series name" field.
6. In the "Series values" field, click on the "Collapse Dialog" button (the small icon to the right of the field).
7. Select the range of cells that contain the data for the second chart.
8. Click on the "Collapse Dialog" button again to return to the "Edit Series" dialog box.
9. Click "OK" to close the "Edit Series" dialog box.
10. Click "OK" to close the "Select Data Source" dialog box.

Now, both charts will be superimposed on top of each other, and you can see all of the data in both charts. You can adjust the formatting and colors of each series as needed to make them easier to distinguish.