You are referencing three fields of handles: resistivity_edit, resistivity_text, and unit_resistivity_text. handles does not have at least one of those fields . Put handles with no semicolon right before you call the line:
handles
relevant_handles = [ handles.resistivity_edit, ............
That will cause all the fields of handles to be sent to the command window so you can determine which one field is missing.
EDIT: On second thought, you can't run the fig file from the current folder panel like you tried. You have to either type F5 or click the green triangle if you're in the editor, or click the green triangle in GUIDE. That's why handles is undefined.
