An example, say we allow backorders and customers order, so we have an inventory of negative 6 items. When we get our inventory in, we'd like to have a field where we can enter the quantity received, and either have a dropdown of Add/Subtract/Set to to update inventory accordingly. Then if we get 50 in, but have 6 backorders, when we enter the 50 quantity, it will correctly update to 44 items in stock.

I also think the last field should be the inventory update, not the "Low Stock" field, as we keep finding ourselves updating this field instead of the inventory field.