Here's a "cute trick" to show this with a global field:
Let's assume you have a field that uniquely identifies each record called "RecordID".
Define a global field called gSelectionID
Define a calculation field, called "cSelected".
If ( RecordID = gSelectionID ; "Selected" ; "" )
Define a value list with a single value: "Selected".
Place cSelected on your layout and use Field/Control set up... to format it as a radio button, selecting the above value list.
Write a script:
Set Field [Yourtable::gSelectionID ; Yourtable::RecordID]
Set up cSelected as a button that performs the above script when it is clicked.
this worked like a charm! thank you!