sum

Hi
Can anyone help.
I have recently manage to get some javascript working (on one record entry in the add screen) and has led me to think...
I have a table orders with fields order, part and quantity and have added a sum quanity on the list page to show the total quanity ordered.
This table only has a few entries and I select all to be inline edited to update the quanity field for eah of the entires.
Is it possible for a sum quanaity total to change as I change the quanity of each entry before I click save all. I need to know the total of the edited quantities before I commit the value to the table.
Hope this makes sense
Gareth