Calculation from subform not displaying in main form

[lscheer]

I have a main form

DriverID
Date
Payments
Charges
Total (=[Payments]-[Charges])

Charges are logged in the form's datasheet-subform where they are totaled in the subform's invisible footer.

I'm populating the Total field in the main form by calling the subform's total value using : (=[Forms]![form]![Payments]-[Forms]![subform]![Charges])

It calculates and displays properly EXCEPT if the subform is empty. (In this case, for some reason, it displays the proper value but only for a split second and then disappears...?)

Any ideas on how to remedy this or a different way to achieve my goal?

 

[AccessBlaster]

Comment removed