All of this looks great! Can I use this method to manage a purchase order's balance?

So for instance, if I receive a purchase order for $500 and I can only bill once a month for $100, I want to be able to keep track of how much is left on the purchase order for me to bill. Sometimes I get paid only for part of what the total of the PO is. Can I enter a purchase order number, then send invoices against the purchase order, and be able to see how much of the balance is remaining on the PO each month.