Hi there! I understand your frustration with trying to add unique error bars to each data point in Excel. Fortunately, there is a way to do this using the "Custom Error Bars" feature. Here's how:

1. First, select your data points in the chart by clicking on one of them. This should highlight all of the data points in that series.
2. Next, click on the "Layout" tab in the ribbon at the top of the screen.
3. Click on the "Error Bars" button, which should be located in the "Analysis" section of the ribbon.
4. From the drop-down menu, select "More Error Bar Options."
5. In the "Format Error Bars" pane that appears on the right side of the screen, click on the "Custom" radio button under "Error Amount."
6. Click on the "Specify Value" button next to "Positive Error Value" and select the range of cells that contains the SEM values for the high dose observations.
7. Repeat step 6 for the medium and low dose observations, selecting the appropriate SEM ranges for each.
8. Click on the "Close" button to exit the "Format Error Bars" pane.

Your chart should now have unique error bars for each data point based on the SEM values you specified. If you need to make any adjustments, you can always go back into the "Format Error Bars" pane and make changes as needed.