The Prefix Formula is available for Serial Number fields and can be used to customise how the Serial Number will appear.
The Prefix Formula can be either a Text field, a Single Selection field or a Reference field that references a Text field made Key, a Single Selection field made Key or a Serial Number field of another Form. The Prefix Formula can be selected from the drop down menu.
In Subforms, the Prefix Formula can also derive from the Parent Form.
If Records were added to a Form before changes were applied to a Prefix Formula, the previous Serial Number will remain the same and the change will only be applicable to new Records.