A workpiece or instrument is declared if: [ \textLSL + U \ \le\ y \ \le\ \textUSL - U ] where (U) is the expanded measurement uncertainty.
“This is where the standard protects both us and the customer,” Anton said. “It keeps decisions objective. We don’t ‘hope’ a part fits. We calculate the odds and act accordingly.”
ISO 14253-1:2017 Geometrical product specifications (GPS) — Inspection by measurement of workpieces and measuring equipmentPart 1: ISO - International Organization for Standardization ISO 14253-1 Decision Rules - HN Metrology Consulting
The next week a supplier pushed back. They claimed the parts fit; they had tested them on their in-house fixtures and saw nothing wrong. The supplier wanted rework rather than rejection. Mara, now tasked with drafting the reply, scrolled through the PDF in her tablet, recalling the standard’s insistence on traceability. She wrote a concise report: measured values, uncertainty budgets, method descriptions, calibration certificates, environmental logs. The decision, she wrote, was not made by whim but by applying ISO 14253-1: measurement results plus uncertainty led to the conclusion. INTERNATIONAL STANDARD ISO 14253 1.pdf
While Part 1 outlines the foundational decision rules, the complete ISO 14253 family includes additional documents designed to assist engineers in calculating and managing these boundaries:
The entire uncertainty interval must lie completely inside the specification limits.
The standard is currently in the stage, meaning it has been reviewed within the last five years and no revision is currently planned. The next systematic review is scheduled, and any potential updates would be announced by ISO/TC 213. As of now, ISO 14253-1:2017 remains the current valid edition. A workpiece or instrument is declared if: [
A key concept is the , also known as the "guard band." This is the zone around each specification limit, extending inward by a distance equal to the measurement uncertainty. If a measurement result falls within this guard band, a clear decision of conformance or nonconformance cannot be made with high confidence. Only when a measurement result is farther from the specification limit than the measurement uncertainty can a clear decision be made. This guard band approach effectively balances the risk of accepting a bad part (consumer's risk) and rejecting a good part (producer's risk).
Geometrical product specifications (GPS) — Inspection by measurement of workpieces and measuring equipment — Part 1: Decision rules for proving conformity or non-conformity with specifications.
It is part of the ISO GPS matrix system, which ensures that specifications (drawings), measurement, and verification processes are aligned internationally. Scope of the Standard We don’t ‘hope’ a part fits
This standard applies to:
Explore how the applies to calibrating your existing shop-floor gauges.
In this zone, neither conformity nor non-conformity can be proven.