If a manufacturer has a high measurement uncertainty (
This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later.
Every measurement contains error. No metrology system, regardless of cost, can provide an absolute "true value." Whenever a part is measured, the result is an estimate accompanied by a range of doubt known as . If a blueprint specifies a shaft diameter of , the specification zone is between . If an inspector measures a part at with an uncertainty of , the true value could be anywhere from (inside specification) to (outside specification). INTERNATIONAL STANDARD ISO 14253 1.pdf
The standard outlines decision rules for proving conformity or nonconformity with specifications. These rules are based on the measurement uncertainty and the specified tolerance limits.
Imagine a traffic light where the color transition is blurry. When a measurement result falls exactly on the tolerance limit, is the part good or bad? ISO 14253-1 provides the answer. If a manufacturer has a high measurement uncertainty
The customer must prove non-compliance to reject a part.
To account for uncertainty, the actual decision limits may be than the specification limits (for proving conformance) or wider (for proving non‑conformance). These are called acceptance limits . Can’t copy the link right now
[ REJECTION ZONE ] <--- [ UNCERTAINTY ZONE ] ---> [ ACCEPTANCE ZONE ] | | Guard Band (g) Specification Limit ISO 14253-1:2017 - Geometrical product specifications (GPS)
ISO 14253-1 operates on the premise that every measurement has an error range. If a caliper measures a shaft as 10.00 mm, the actual size might be 9.98 mm or 10.02 mm. This range is the , typically estimated with a coverage factor (usually $k=2$ for a 95% confidence level).