I have a table called Inventory (table1 - PK=INVID) that contains all inventory ID numbers and descriptions. I have another table called Inventory Transactions (table2 - FK=INVID) that gets updated through a form. When a new transaction is made in table2, I want the transaction amount to get added or subtracted to an OnHandQty field in table1. I tried having table2 (transaction table) as the main form and then table2 as the subform, but I couldn't get table2 to update. Any help would be appreciated.