This white paper deals with the perfect order metric concept, important in purchasing and warehousing. You want to fill the perfect order.
I just got an order from Vitacost, and the packing slip said that one item had not been picked. Not perfect. i had to call them, wasting an hour, to get the other item shipped. They were very nice, though. Shows you how hard it is, and how costly.
Supply Chain and Logistics 