OK, something weird is going on with that form. None of the element JS is loading, which is why the calc doesn't work (and various other things).
But ... if I set that joined group's access to "Public" so it displays, then everything works.
NOTE - the way you have that join set up probably won't work. One end of a join MUST be the PK (Primary Key) of the table. So you can't use shared foreign keys, where neither of the fields in the join are the PK.
However, I'm not sure if that is anything to do with why having on group with ACL's making it not usable is affecting the JS loading. I haven't managed to duplicate it here, but I'm still working on it.
-- hugh