refreshing from subform

[xxyy]

Dear All,

I'd like to ask you help me in the following issue (sorry, I'm a beginner):

I have got a simple form - subform structure. There's a box that calculates the sum of the some fields. Those fields (which the calculation bases on) are on the subform.
If I change the values of the mentioned field on the subform, the calculation will not be updated (un less I change the record on the main form or I reopen the form)
I tried 'AfterUpdate' and 'Current' but as if I haven't used them, they couldn't help.

Please help and give me a simple solution.

Thanks in advance,

Sz.Cs.

 

[DB7]

AfterUpdate Event, of control on Subform
Me.Parent.Refresh
or
Forms!frmMain!txtSum.requery.

Or on exit of Subform Me.Refresh