I did a presentation on this topic for the Acrobat Users Group (BTW: another good forum for information). They recorded it. You should be able to get at the presentation here:
Thanks, I looked at it -- and I could not make it work.
If I click on a numeric box then in the formula area above type in what you provided:
Sorry, I am not a programmer. I also inserted this code into the xml and nothing.
The correct way is: