Why - I hear you ask...?!??
The first the screen that the user will use is simply to scan a barcode and display the decoded ID in a textbox - this doesn't need to be linked to a table at this stage.
This is then saved in a variable which I use in a script on the next layout that displays data (eg. SELECT Order WHERE OrderID = $ScannedCode
When I add a textbox to the first page via Field Chooser - these are linked to underlying tables - also when I scan a barcode it asks me if I want to save the record (????) - nothing needs to be displayed at this stage
Hopefully this makes from my crazy head...?!?!