The sixth in this series of articles by Stephen MacDonald on individual aspects of the assessment of uncertainty of measurement considers the impacts created when contributors are not measured in the same units.
In this article we continue towards understanding the application of measurement uncertainty to our assays. We ended the last article by combining uncertainty contributors into an overall combined uncertainty. We only considered contributors measured in the same units. In this article we will cover the approach when all contributors are not measured in the same units. Second, we will see if we can quantify the proportion of the overall uncertainty each contributes, and in doing so give us a mechanism to monitor and reduce our uncertainty. Finally, we will apply the coverage factor to state our expanded uncertainty.
If we return to the diagram (Fig 1) shown in the previous article in this series, in the February issue, we are ready to head into the final stretch of finalising our uncertainty budget, checking performance and periodically re-evaluating the overall budget.
Order of magnitude and measurement units
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