The ‘ Guide to the Expression of Uncertainty in Measurement ’ (GUM) has been in use for more than 20
years, serving its purposes worldwide at all levels of metrology, from scientific to industrial and
commercial applications. However, the GUM presents some inconsistencies, both internally and with
respect to its two later Supplements. For this reason, the Joint Committee for Guides in Metrology,
which is responsible for these documents, has decided that a major revision of the GUM is needed.
This will be done by following the principles of Bayesian statistics, a concise summary of which is
presented in this article. Those principles should be useful in physics and engineering laboratory
courses that teach the fundamentals of data analysis and measurement uncertainty evaluation.