Rational
On large inventory (with a lot of lines), it may be difficult to fill it by searching the right line and set the quantity. A common technique is to count the products. This means that the user just inform the system when he see a product in the location. Then the system increase the quantity for this product by one.
Proposal
We add on the stock module a new wizard for the inventory. The wizard is a loop over two views. The first view ask for a product (or a lot). The second displays the product and asks for the quantity to add (by default 1 unit of the default UoM). It shows also the new quantity value (which is the sum of existing line quantity and the quantity of the form). If the there is no line that match, a warning will ask to create it or not.
In case of error, the user may still edit the line with the correct quantity or he can remove all the lines and click on “Complete Inventory”.