Problem with text box calculation

[pikou]

Hi all,
I have a form tha is based on a table and a subfrom on another.The two tables have a valid 1 to many relationship and all is well record viewing wise.
Now I have some financial data like the fee that was agreed upon on the main form on a text box .On the subform the user can enter the payments made on variou dates.
What I want is to be able to have a text box on the main form that will do the subtraction (fee - all the various payments) and display that on the main form.Is this possible cause I cant seem to be able to do it and if it is not, is there another way for this to be done.
Thank you very much for your time

 

[llkhoutx]

Sum the payments in a control (txtPaymentsTotal) in the footer of the subform, the control source of which is "=sum(me!PaymentscontrolName)", but without the quotation marks .

On the form in a control create an unbound control (txtBalance), the control source of which is "=nz(me!fee,0) - nz(forms!MainFormName!subFormName.form.txtPaymentTotals,0)", but without the quotation marks.

The nz function must be used because if ther fee or payments total is null, the equation will not calculate.