Is it safe to assume you are using a fairly recent version of Monarch?
Have you looked at the features within the Monarch Summaries?
If you can set up your seven Fields (Table Columns) as MEASURES in a summary definition you can change the properties of the measure to make a variety of calculations. Once you have added a field as a measure just right mouse click on it in the measures window and the properties window will appear.
You can do this for the same field several times if required simply by setting it as a measure several times and setting different properties for each occurrence.
The Summaries definition offers 2 variations on the Standard Deviation calculation and the option to define your own calculations.
However, it does occur to me that you may be looking to obtain a standard deviation calculation from the figures in all seven columns in the table as a single figure. (I could read your question two ways.) In that case I think you will need to combine the numbers first into one column and that would, I imagine, require an intermediate process to export what you have and then re-process it with another Monarch model. Unless there is a way to achieve that from the Monarch process you already have.
Difficult to know without seeing the report and what you need from it.