Creating pivot table measure using pivot table data

[alandilworth]

Hello, I am looking for advice on how to use data in a pivot table in a measure.  For example, in the table below I am trying to create an 'Average' column that displays the average of all 'Sales' inside each 'Grouping'.  The ‘Grouping’ column here is a calculated measure.  For each grouping I want the sales in the 'Sales' column to be added together and divided by the number or rows in the grouping to come up with the average.

Any help will be greatly appreciated!