Depends - are you talking about two different fields which contain the same month? Like Sales_Year & Revenues_Year?
Then I suggest working with triggers. Choose 'Select Field', put in the name of your second listbox/field and in the selection box:
Don't forget to include the same trigger 'On Change' if necessary.
Let me know if this helps you.
See attached example. See the actions on the OnSelect trigger of Field Prod1 to see how this is done.
Test0707LB.qvw 135.8 K