Readers of this column will be familiar with the subject of measurement uncertainty since I comment on it from time to time, as I did last month. Those readers that have not been that interested in it will certainly run across it on reports from their calibration sources. All things considered, it is an element that permeates measurements of all kinds and without a statement about it, the numbers on a report are just readings with little credibility.
Gage and instrument calibration is a specialist branch of dimensional metrology governed by a number of published standards, the most popular being ISO/IEC 17025. This standard and supporting documentation stipulates that measurement uncertainty must be included in reports issued by accredited laboratories and outlines how it should be calculated. The meaning and application of uncertainty often brings up questions which I hope the following notes will provide answers for.