by Hening Huang
As a practitioner in the field of measurement science, the author strongly concurs in the need for revision of the GUM (Guide to the Expression of Uncertainty in Measurement), as it has some shortcomings and limitations. This paper is the first one (Part I) in a series of two papers (Part I and Part II) designated to provide practitioner’s perspective on the GUM revision. This paper (Part I) focuses on two key problems: (1) inconsistency in GUM’s two definitions of measurement uncertainty, and (2) limitations of GUM’s method for calculating the expanded uncertainty. The first problem can be solved by defining ‘uncertainty of measurement’ as the ‘probabilistic error bound’ based on the law of error. The second problem can be solved by either of two alternative approaches for calculating the expanded uncertainty. We argue that, on the one hand, a revised GUM should correct GUM’s shortcomings and address its limitations, thereby providing better guidance; on the other hand, it should minimize potential impact of the revision on GUM’s current practice; both should contribute to the success of the GUM revision. Part II will examine four examples of the GUM in detail using the two alternative approaches, and describe the resolutions to the Ballico paradox due to GUM’s method for calculating the expanded uncertainty.
