Update field

[Valerie]

I am just about finished building my inventory database
(based on the Inventory Control template in Access), but a
question just came to mind. "On Hand" shows current
inventory based on a calculation of # received + # used.
However, I want to create a new field for starting
quantity, and I don't want to give it "false" purchase
orders to 'acquire' our initial inventory. If I do this,
how can I tell my On Hand field to take into account the #
in Iniitial Count? I can't figure out where the
calculation behind On Hand was created, so I don't know
how to mess with it.

Thanks.

Valerie