At Microsoft, Pam has a new GP 2013 Weekly Topic: Purchase Order Tolerance
GP2013 Weekly Topics; Purchase Order Processing
Weekly Topic: Purchase Order Tolerance – Inside Microsoft Dynamics GP
Sales, Purchasing & InventoryTips & Hidden FeaturesGP 2013
Archived post from 2013. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.