How to give unique article numbers for each article with attributes?

Eg:

Article: Bicycle "Fully"
Color "black" size "S" article number 300021
Color "black" size "M" article number 300022
Color "black" size "L" article number 300023
Color "black" size "XL" article number 300024
Color "black" size "XXL" article number 300025

Color "yellow" size "S" article number 500055
Color "yellow" size "M" article number 500056
Color "yellow" size "L" article number 500057
Color "yellow" size "XL" article number 500058
Color "yellow" size "XXL" article number 500059
aso.

I've installed the extension "stock by attributes": http://www.zen-cart.com/index.php?ma...roducts_id=310
But somehow, I can't see/find the option (input field) to enter the unique article number while adding/defining attribute(s) for this article.

Thanks