From the absolute to uncertainty [metrology]

The history of the electrical units since 1948 is reviewed. The change from the conventional methods of expressing accuracy through the uncertainty methods is followed. Included are some of the attitudes and practices as instruments and standards have become more precise. The development of metrological uncertainty is reviewed. The effects of international recommendations and standards are presented. The necessity of knowing not only the value but its uncertainty is expressed; the process of developing coordinated values for the fundamental physical constants is reviewed.