Automatically adding/expanding new row in MS Access forms

Question

I am trying to build an invoice form in which the user has to select an item and when ever the item is selected from the combo box, a new blank row should be added at bottom as shown in the screen shot below.

I have seen that the Northwind sales database has done same thing but I don't know how to implement it. As per my search, they have build form (below screen shot) and put it in Order Detail (Subform), but what is the logic behind automatically adding of new row at last?

Answer 1

http://www.accessforums.net/forms/automatically-adding-expanding-new-row-ms-access-50531.html

above link give you complete solution