Display total as user enters sales data in a form

[Demerit]

I have a form named "FrmSales" which includes a subform named "InvoiceDetailsSubform"
In the subfom, I have the following cotrols: Productname, Unit, Qty, UnitPrice, OUP and Amount.



On the form sales I wish to have a control that displays the total of the control "Amount" as the user enters the sales data.

What i did is: I created a control on the form footer of the form "FrmSales" and in the control, I attached the code

=Sum([Forms.FrmSales.InvoiceDetailsSubform.Form.Amount])

But when i return to Form view, I get an error display in the control.
Please what is not correct with what i have done?

[Bob Fitz]

What I think you need is this:
A text box (lets name this txtSubFrmTotal) in the footer of the sub form with its Control Source set to:
= Sum([Amount])
Another text box on the main form (lets name this txtMainFrmTotal) with its Control Source set to:
= [InvoiceDetailsSubform].Form!txtSubFrmTotal

[Demerit]

Thanks Bob Frtz its working. In the parent form i actually used this

=[Forms].[FrmSales].[InvoiceDetailsSubform].[Form].[TxtSubformTotal]

in the control named TxtMainFrmTotal.

[June7]

Alternatives

1. subform set for datasheet view, open the form/subform normally (not in Design view), click on the subform then click the Totals button on ribbon to reveal a Totals row below last row

2. subform in continuous view and arrange controls to look like datasheet, textbox in subform footer will now show