You can use Line_Column type of chart on the custom Chart
Tab. This will allow you to add either the mean of the std
dev. Show data as
23 39.5
34 39.5
45 39.5
56 39.5
where 39 is the average.
You will have to add the other line yourself using the
drawing toolbar.
Remember to select the whole chart including the Added
line and select Draw, Group on the drawing toolbar.
Create a Line-Column chart then right-click the columns in
the chart and select format data series. On the Y error
Tab you can choose to add a stddev line default set at 1
to the chart. If you choose the above and below it shows
the average as well.
