How do you set up a secondary units ledger associated with the AA ledger?

How do you set up a secondary units ledger associated with the AA ledger?  Client is converting from World to A9.1, and are currently using AA AU and A# for each transaction.  On the A# LT transaction, the amount is zero and the Units are the number of pounds associated with the dollars in the AA and the heads in the AU.  The A# is set up in the LT master, but the Units LT  field is blank.  When they post the units for the A# it adds them to the AU's and messes up the number of heads.  I