intelligent text in DRAFT just allows to call out values of attributes but I think you can't define any calculations with those.
If you want to avoid the necessity to maintain the required sum in Design with a macro a circumvention might be:
Allocate an UDA of type NUMBER/REAL to a Draft item like GLAB or any suitable master element e.g. a View, if you have one table per view only.
Write a macro which performs in Draft the required calculations and assigns the result to this UDA.
If you want to avoid that users have to start this macro on request smuggle in as payload a call to this macro into another macro e.g. for starting a PLOT, UPDATE a VIEW/SHEET or whereever .
