This addon changes the way that the Stock input works on the product adding/editing page in Admin. It solves a race condition for some shopowners who sell their products both online and offline (eg in a shop) or those who regularly get new stock from their supplier.

The old system
You have 3 in stock.
You get 10 more from your supplier.
You open up admin/catalog.php, find the product and open the editing screen.
You insert 13 into the input box.
In the meantime, someone has bought 1 of this product.
You click save.
Your admin tells you 13 "in stock", yet in reality you have 12.

The new system
You have 3 in stock.
You get 10 more from your supplier.
You open up admin/catalog.php, find the product and open the editing screen.
You insert 10 into the input box.
In the meantime, someone has bought 1 of this product.
You click save.
Your admin tells you 12 "in stock" as the system adds on 10 to the live stock count.

This addon requires 1 (ONE) line of code to be added to one admin side file. It is, therefore, NOT a "no core code change" addon unfortunately.

If the price of this addon does not suit your business, contact me anyway. I'm sure we can come up with a good deal that suits each other. Prices are not set in stone.