MEASUREMENT UNCERTAINTY AND PROCEDURES OF CONFORMITY ASSESSMENT

A conformity-assessment procedure is intended to ensure that a product or process meets a specified requirement. We discuss legitimate expectations of both the 'producer' and the 'consumer' for the performance of a conformity-assessment procedure and show that, in the typical case where a producer repeatedly send goods to a single testing authority, the form of expression of measurement uncertainty described in the Guide to the Expression of Uncertainty in Measurement is inconsistent with these expectations. The difference between the behaviours of constant and random components of error in this typical situation means that the sum of these components cannot be represented by a single figure of 'standard uncertainty'. In this context, measurement uncertainty is better described by the underlying variance of the random component of error and worst-case values for the constant component.