Apache Jmeter testing checkout process (every time the same order number)

Hi.

Now I,m trying to create checkout process perfomance testing using Apache Jmeter.

I create script for testing, but I find one problem. This script from Jmeter evety time creates order with the same number.
I think, that I need to update some setting ( like cookie or VIEWSTATE) durring the script, but now my search is unsuccessfull. May be somebody know, what parameter I need to clean while checkout process to upgrade onder number every time otder runs?

Sergey.

anybody?