Every database application uses combos for selecting a value from a lookup table.
By setting the combo's LimitToList property to Yes, you can use the NotInList event to append a new entry to the lookup table . You can then use acDataErrAdded to cause Access to find the new value. Opening a form is unnecessary, as the user has already typed the new value. The function below verifies the entry and appends it to the lookup table. This function identifies the lookup table from the combo's RowSource property.