The newest GP2013 Feature of the Day:Update Back Order Item Qty in Field Service
Feature of the Day:Update Back Order Item Qty in Field Service – Inside Microsoft Dynamics GP – Site Home – MSDN Blogs
Sales, Purchasing & InventoryTips & Hidden FeaturesGP 2013
Archived post from 2012. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.