Adding a Function to a Subform
To add a function to a subform:
Click the subform to which you want to add the function and select Form, Create, Function .
The Application Tree View browser switches to the Logical Hierarchy view, and the function appears in the tree as a child object of the subform. (Functions do not appear in the tree if set to the Physical Hierarchy view.)
Right-click the function in the tree and select Edit ER.
The Event Rules Design form appears.
Create the logic for the function as you would for an ER.