What about_
uicontrol('Style', 'edit', 'String', ['22.4 mm', char(178)])
But this is limite to specific fonts and only some numbers. For a general method it matters, if you only want to display the super scripted text or edit it:
uitable('Data', {'<html>22.4 mm<sup>2</sup>'});
But of you edit this table cell in the GUI, the HTML control keys appear confusingly.
