[dba-VB] VB2005 DatagridView with unbound calculated fields

Hi All
 
I have a form with a parent and child grids. On the child grid I have 2  
unbound calculated fields. And everything works fine. What I need to do is add a  
subtotal field for 1 of the calculated fields. And the subtotal to appear  in 
a textbox on the form for each parent.
 
Anyone seen this before? Any sites that may explain how to do it?
 
TIA
johnc