<<calc !!due -1>>
<<calc !!due -!!mynow>>
<<calc !!due - !!mynow>>
<<calc !!due -<$view field="mynow"/> >>
I think you must use a text reference {{!!fieldname}} or fieldname
But never a !!fieldname
Check the calc doc and look for an example.
Tony
<<calc !!due - by:!!mynow>>
a value or a TextReference serving as the operand if the operation does not define any