This part of ISO 14253 outlines the main assumptions behind the theoretically ideal decision rules established in ISO 14253-1. It discusses why these rules have to be the default rules and what considerations should be taken into account before applying different decision rules. This part of ISO 14253 applies to all specifications defined in general GPS standards (see ISO/TR 14638), i.e. standards prepared by ISO/TC 213, including - workpiece specifications (usually given as specification limits), and - measuring equipment specifications (usually given as maximum permissible errors).