e.g. '''=[@section.''expense''.id@_''Total_Amount'']-[@section.''income''.id@_''Existing-funds''_''Amount'']'''
If you need want to display data in the head of a section (row 0) from another section you can use the following:
@xml.customfieldname.sectionnodename.rownodename.columnnodename@
==Validate values when saving the worksheet==