GPS – Use of measurement results. Conformity assessment


Conformity assessment

The rules for determining when the characteristics of:

are in conformance or non-conformance with, respectively:

taking into account the uncertainty of measurement are specified in GPS standard ISO 14253-1:1998.

Also included are rules about how to deal with cases where a clear decision (conformance or non-conformance with specification) cannot be taken, i.e. when the test uncertainty interval is within a measurement uncertainty of a specification limit.


Three steps for conformity assessment

1      Validate limits on measurement capability

Before assessing compliance of the entity with product specifications, it is first necessary to assess compliance of the actual measurement capability with measurement specifications.

Usually this means ensuring that the actual measurement uncertainty is less than the agreed target (or maximum permissible) measurement uncertainty. The GPS standard ISO/TS 14253-3:2002 emphasises the importance of reaching agreement between customer and supplier about measurement uncertainty, preferably even as early as the pre-contract stage of a commission, usually in terms of an agreed target (or maximum permissible) measurement uncertainty.

Following actual measurements (that is, at the verification stage), normally it is the party providing the proof of conformance or non-conformance with a product specification or measurement equipment specification, i.e. the party making the measurements, which states the actual measurement uncertainty, according to GPS standard ISO 14253-1:1998 [§6.1].

2      Check location of uncertainty interval

3      Assess risks for decision-errors


lecture* – Example: Vehicle closure panel assessmentbil


  • ISO/TS 14253-3:2002 Guidelines for achieving agreements on measurement uncertainty statements
  • ISO 14253-1:1998, Geometrical Product Specification (GPS) — Inspection by measurement of workpieces and measuring instruments — Part 1: Decision rules for proving conformance or non-conformance with specifications.

Verification process

The verification process is to “verify the workpiece/feature characteristic to the specification operator defined by the actual GPS specification” according to ISO/TS 17450-2.  As such, the verification process takes place after the specification process. The final step of the verification process is when the measured value is compared with the GPS specification.

ISO/TS 17450-2:2005 Geometrical product specifications (GPS) – General concepts – Part 2: Basic tenets, specifications, operators and uncertainties

GPS – Specification of demands on Measurement System
GPS – Presentation of measurement results


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