Inventory Software ::. Reorder Level .::

HI
I am a VB programmer and having a problem while developing an inventory application. There is need a Reorder Level integration in my application. Can anyone tell me how can i program this Reorder Level Indication. Mean to say that
If the number of anything in my inventory goes down from Reorder level. then the program gives you the Indication. How can make that in my application.

Thanks
M.F.Aziz