Worksheet To Track Inventory

I'm trying to make a worksheet to track inventory, not for sales but for tracking how many supplies are on hand in storage rooms, closets, etc. The worksheet will be used by as many as 20 different users probably on a network.

Because it will be used by many people, I'm trying to see if there is a way that the worksheet can be updated after every save. In particular, the amount that are "on hand".

For example, say there are 10 of a particular item on hand to start. Joe takes 2 and goes to record it on the worksheet. He inputs the 2 he takes, which now show that there are 8 on hand remaining. He saves the worksheet. Then, Jerry comes and takes 2 and goes to record it on the worksheet.

I can't figure out how, or if it's possible, to have the worksheet show Jerry that there are 8 on hand to start, not 10. So that when he takes his 2, it should show that there are now 6 on hand remaining. I've attached an example worksheet.