Calculated Field In Pivot Table

[nailers67]

I have attached a sample file that I am working with and I am trying to figure out how to an average calculation in a pivot table, but it is not working properly.

What I want to do is take the week number with is the range of weeks the report was created (for 3 weeks).

I want to take the total number of sales which is summed up in the data range of the pivot table and divide that by 3. So I created a calculated field, which is "= ITEMS / WEEK". Now I know, that the pivot table totals up the week (which is not what I wanted) and I cannot create a cell reference in a calculated field. This report can be run for any number of weeks so I cannot just put the 3 in the calculated field.

Is there a function that I can use in the calculated field to do what I need it to do? I tried =ITEMS / MAX(WEEK). I didnt think it would work. The number in the Weeks column will always be the number of weeks in which the report was run for.

If I did not explain this good enough, let me know and I will try to clarify it.

Thanks in advance.