how to calculate data of a particular colomn in listview ?

hi all

I am storing data in a listview before SAVING. I want to calculate (sum) one colomn in listview when I pressed a command button and same way if I press other command button it should MINUS particular amount from that total. I want result (total) in particular text box.

how can I do this?

plz. help. Thanks in advance, guys.

kaushal