Believe me, I agree with you, but this is how they want it done. I know the ok button does nothing, because I don't have a clue as to how to approach this.

If the user does not select anything in combobox1, than by default everything in the combined tab will be used (or summed up). If a user selects an ISD, but no specific district, than all districts will be used, and so on. Does that make sense?