Scripting Conflict With Field Names

I have a form with the following fields: Item Code, Desc, Piece per Unit, Qty Needed, Cost per Unit, and Total Cost. We have named each of the Qty Needed fields (numQty_xxx) where xxx is the part number. Here are two of our part numbers: 90014 and 90014-000-2919. My script works perfect for 90014, but when I get to those like 90014-000-2919, the dashes between each set of numbers acts as a subtraction instead of a dash mark. Here is the script I am using: calculate*numQty_90014*unitCost Lang=FormCalc Run At=Client. How can I get this to work?