Calculated Field Creation (Subtraction of VARCHAR data possible?)

Hi All

(Using Cognos 7.3 Admin)

Not exactly a newbie to Cognos anymore really but have not created “Calculated Fields” yet but need to and have run into a problem.

I need to create a simple calculated field that will subtract a “received quantity” field from an “order quantity field” in one of our db’s. However this information is ingested each night from our financial db into a table in our “biblio” db and the fields are varchar. I assume this is why I’m not seeing a way to subtract these fields in the “available components” list when I try to create the calculated field.

Is there a way I can “cast” these fields as numbers or otherwise “fool” Cognos into seeing them as numbers so I can subtract them?

Trying to avoid changing the table itself as it would involve changes in sprocs & other reporting.

Any help would be MUCH appreciated.