Refinements to traditional approach
The Type A uncertainty may be calculated (as the standard deviation) from the variation among the many "replicates" (repeats) of the same measurement. Many Type B uncertainties, for example, can be eliminated by calibration (just correct for the known, ca...
Ratio requirements need to be re-examined
Early in the 20th century, establishment of laboratories devoted to measurement science, such as the U.S. National Bureau of Standards, now the National Institute of Standards and Technology (NIST), focused formal attention on measurements as a subject wo...