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To add error bars (for the Y values in an X-Y chart):

Add two columns (or rows) alongside your data; one column contains the value for error above each data point, the second column contains the value for error below each point.

Right-click the data series in your chart and choose Format Data Series

Go to the Y Error Bars tab

Select the Custom radio button

Point the + field to your column of error above values

Point the - field to your column of error below values