This thread helped me understand Fields a lot better years ago. Field format has changed a little over the years. Best way to figure them out is create what you want in the command's dialog box keeping an eye on the Field expression at the bottom. Make a change and observe the changes in the Field expression at the bottom.
The "%ps" wasn't part of the format back when Jenna started this thread it's for adding a Prefix and/or Suffix as in "%ps[prefix,suffix]"
The "qf1" which was limited to a couple preset scales has been replaced by %ct8[scalefactor] that you can set to any scale you like.