GB/T 18779.4-2020

This standard provides the foundational principles for establishing decision rules in dimensional metrology by distinguishing between functional limits (the actual boundaries within which a workpiece must function) and specification limits (the tolerances defined on engineering drawings). It is applied in manufacturing quality control and inspection processes, particularly when using coordinate measuring machines or other precision measurement equipment to determine whether a produced part conforms to its design requirements. The standard helps engineers and metrologists account for measurement uncertainty when making pass/fail decisions, ensuring that functional performance is prioritized over strict numerical compliance.