Calculate actual hours to FTE in pivot

[kammend]

I have a timesheet that contains all worked hours for all resources. It also contains the role of that resource.
What I'd like to create is a chart based on a pivot in which the number of FTE is shown.

In another table I have calculated the number of hours per month (working days * 8 hrs)

Can I create a pivot based on 2 tables or is there a way to have the number of working hours into the TimeSheet table?

[kammend]

The idea is that when in a month my resources worked 400 hours and the standaard number of hours in that month is 160 for 1 FTE, I can have the pivot calculate the number of FTEs in that month (400/160 = 2,5)

Since the number of workable hours in a month in not a constant value, I have calculated that in a separate table. (See attachment)

This all should result in a graph showing the number of FTE each month, rather than the hours worked.... So, the calculated field in the pivot is the only field that is displayed in the graph...

Can this be done?