Brief
The behavior of this field should depend on the production counting method selected in the production order.
If none method is selected then it should behave as it always did.
If some production counting method is selected the the field not be editable and should always point out the produced quantity indicated be the production counting mechanism.
Also add the following description to the field:
"This field is editable only if no production counting method is selected. Otherwise this field will show the produced quantity indicated by the data passed to the production counting mechanism"
Suggestion: I think that just keeping it in sync with the production progress data structure should be enough.