Add calculated item to pivot table

Dear All

Attached is a worksheet example, of my beauty salon with 5 therapists.

The input sheet - is the shhet into which I input data on a daily basis.

Weekly inc - This sheet shows the total that each therapist made in apivot table based on the input. The week numbers are 1 to 52 (or 53) depending on each financial year (07/08, 08/09 etc).

What I want to do is either have another pivot table or to add an calculated item to the weekly inc pivot table showing me how much commission each therapist took each week? This is to be done automatically by excel.

This commission is calcluated by using the target comm figures - E.G. Leanne's target is £480 - so she has to earn £480 a week before getting a commission. So if in a week she earns £500 - she will get a commission on £20 (£500 - £480). The commission is 10%, so she will earn £2 that week.

Any help would be much appreciated.