Decision Rule

Sheffield Calibration Services Ltd is a dimensional calibration laboratory. We work to an international standard, ISO/IEC 17025:2017. This standard has a host of requirements to be fulfilled by the laboratory to ensure the laboratory can garner client confidence, operate competently and ensure the validity of results.

Clause 7.8.6 of ISO/IEC 17025:2017 requires that when a statement of conformity to a specification or standard is provided, the laboratory shall document the decision rule employed, considering the level of risk associated with the decision rule employed, and apply the decision rule.

Furthermore, this decision rule must be agreed with the customer and also reported with the results on the calibration certificate. Note: - it is not mandatory for laboratories to reportstatements of conformity. These rules apply when a laboratory has agreed with a customer that such statements will be reported, or when the calibration specification details that these statements are required. Certifcates can be provided without statements of conformity but this then means there will be no pass/fail result on the certificate.

With the above in mind the laboratory has chosen to apply the simple acceptance shared risk rule to all calibration certificates to meet the specification requirement. The rule to be applied can be found in clause 8.2.3 of the metrology guide JCGM 106 2012 – the role of measurement uncertainty in conformity assessment.

Please see the below statement from section 7.8.5.1 from our current Quality Manual:

The laboratory has implemented a policy to cover the requirements of this section. (POL 7.8.6) The simple acceptance rule is preferred by the laboratory and applied unless instructed by the customer at the contract review stage. When the customer or a specification requires a different statement of conformity to the laboratory documents the decision rule employed, taking into account the level of risk associated with the decision rule employed, and apply the decision rule. In such cases the laboratory manager is responsible for reviewing and applying the decision rule and a level of risk. The level of risk includes the uncertainty of measurement and is defined as providing a 95% level of confidence in the uncertainty of measurement and has been carried out in accordance with UKAS requirements.

To meet the requirements of the Rule and prove the level of risk has been considered and accounted for, the laboratory will require an uncertainty budget for all features measured and reported on a calibration certificate. The uncertainty value must be no greater than the relevant tolerance applied from the appropriate product specification.

The Rule will replace our previous method of reporting accuracy statements which did not consider uncertainty values before the implementation of ISO/IEC 17025:2017.

There is a plethora of possibilities for methods to take measurement uncertainty into account when applying decision rules. These are sometimes imposed by Regulators, some are industry-based norms, others required by second party specifiers and can be agreed with the customer at the contract review stage but where decision rules proposed by the customer are not considered appropriate or applicable to the results being reported, then the laboratory will need to discuss this with their customer to ensure that the outcome is fit for purpose.

Our full policy on the decision rule can be seen below.

Please feel free to contact the laboratory if you have any concerns regarding the decision rule and how to move forward regarding the application or non application of the Rule to future calibrations.