When the measure is placed on the view, the aggregation can be changed. Right click on it and select Measure-->Average. Another instance of the measure can be placed on the view, and to find the Standard Deviation, right click and select Measure-->Ste. Dev.
Then, a calculated field can be created to find the +/- on the std error.
Hope this helps!
Sorry I wasn't clear in the original message. The line I want to plot is the average of the averages.
For each user, take the average. Then find the standard deviation and average of those averages.
I understand how to create a calculated field, but I can't figure out what to put to make the average and standard deviation of the user averages.