[Scribus] Calculating values of PDF fields

[Marvin Dickens]

Hello,

I am trying to calculate a field value in a PDF form I am creating
with Scribus. How do I do it? If I go:

PDF options---> Field properties--->Calculate---> 
Value is the product---> Pick---> Select available fields

There is nothing to select under "Select available fields" even
though the fields I want to select from exist. I suppose my
question is how do you make fields selectable?


Best regards

Marvin Dickens
Alpharetta, Georgia  USA