Calculate the value of a field derived from the values of other fields. Requires a
MODIFIER indicating whether
the fields should be added or subtracted from the current total.
"CALCULATE > 'destination_field' < [modifier 'source_field', modifier 'source_field', etc]"
modifier is either of
-. If you want to change the sign of the values in a column,
before further arithmatic, you'll need to do this sort of script:
"CALCULATE > 'destination_field' < [modifier 'source_field', modifier CALCULATE < [- 'source_field']"
"CALCULATE > 'total' < [+ 'income', - 'expenses']"
This is still very rudimentary. Enhancements should stick to basic
reverse Polish notation arithmetic.