What’s New in Visio Services 2013 - Visio Services Quick Guide - page 115

30. Right-click on one of the shapes and select the option 'Edit
data graphics.'
31. Click on 'New Item. . .' and, from the Data field, select the
'More Fields. . .' option, as shown in Figure A-20 .
Figure A-20. Choosing custom fields
Under the Field window, select Custom Formula and type
the following in the Custom formula: input, as shown in
Figure A-21 . Click OK:
=({Budget}-{Spent} >0)
Figure A-21. Creating custom formulas for custom fields