Hey Don,
It shouldn't be an issue, but it depends on the control flow.
For example, before Field 5 can be calculated Fields 1-4 cannot be empty and must have integers. Make sure Field 5 gets calculated at the end after all the other fields are finished being calculated.
Even try to add a button for testing purposes 'Field 5 Calculate' once the screen has Fields 1-4 with integers, click the button to execute Field 5 calculation.
Give that a shot and let me know how it works out.
-- Mortaza