It is now becoming recognized in the measurement community that it is as important to communicate the uncertainty related to a specific measurement as it is to report the measurement itself. Without knowing the uncertainty, it is impossible for the users of the result to know what confidence can be placed in it; it is also impossible to assess the comparability of different measurements of the same parameter. This volume collects 20 outstanding papers on the topic, mostly published from 1999-2002 in the journal "Accreditation and Quality Assurance." They provide the rationale for why it is important to evaluate and report the uncertainty of a result in a consistent manner. They also describe the concept of uncertainty, the methodology for evaluating uncertainty, and the advantages of using suitable reference materials. Finally, the benefits to both the analytical laboratory and the user of the results are considered.

Validationofmeasurementmethodshasbeenusedforavery ciated measurement uncertainty? The answer must be: no. longtimeinchemistry. Itismostlybasedontheexamination Therecanneverbeamechanismorrecipeforproducing - of a measurement procedure for its characteristics such as tomatically 'valid' results because one can never eliminate precision, accuracy, selectivity, sensitivity, repeatability, re- theskills, theroleandtheresponsibilityoftheanalyst. producibility, detectionlimit, quanti?cationlimitandmore. ISO 9000:2000, item 3. 8. 5 de?nes validation as 'con?r- When focussing on quality comparability and reliability mation by examination and provision of objective evidence in chemical measurement, the ?elds of interest to this Jour- that the requirements for an intended use are ful?lled'. The nal, one stumbles into various interpretations of the term revised edition of the VIM ('VIM3'), is likely to ?ne-tune validation. It is one more example of a term which is used thisde?nitionoftheconcept'validation'tobe'con?rmation sometimes very consistently, sometimes very loosely or in- through examination of a given item and provision of - deed ambiguously. Since the term is very common in the jective evidence that it ful?lls the requirements for a stated chemical community, it is important that its meaning be intendeduse'. nd clear. Turning to the 2 edition of the International Vo- Lookingatsimplepractice, manypeoplearelookingfor cabulary of Basic and General terms in Metrology (VIM) aformaldecisionthatagivenmeasurementmethod automat- (1993), surprisingly we do not ?nd a de?nition. Webster's ically gives them 'valid' i. e. reliable results. One wonders Dictionary of the English language (1992) tells us that val- what this has to do with 'stated intended use'. Reliab- idation is 'making or being made valid'. Obviously valida- ity clearly is a property of a measurement result.

Metrological traceability of chemical measurement results means the establishment of a relation to metrological stated references through an unbroken chain of comparisons. This volume collects 56 outstanding papers on the topic, mostly published in the period 2000-2003 in the journal "Accreditation and Quality Assurance." They provide the latest understanding, and possibly the rationale why it is important to integrate the concept of metrological traceability including suitable measurement standards such as certified reference materials, into the standard measurement procedures of every analytical laboratory. In addition, this anthology considers the benefits to both the analytical laboratory and the user of the measurement results.