I'm using Zen Cart 1.3.9h and I'm stuck.

I want to add an attribute that will add a set dollar amount for the attribute and a percentage discount on the product.

It's for fundraising purposes: Buy this product at regular price, or support the cause by purchasing a 5% discount for $5 dollars.

I keep trying to adjust the Price Factor and Offset using both positive and negative numbers, which appear to show the effects of the changes when viewing the product in edit mode, but when I add it to a shopping cart, I either get the same regular price for the product, or an increase in price for the product.

The only thing that works correctly for me is the One Time price for the attribute.

Can someone tell me what I'm doing wrong? Perhaps a better explanation of Price Factor and Offset would help me. It's not clear to me what they are or how they work.