What kind of uncertainties are provided with calibration reports issued by the Mechanical Metrology Group?
In the past, it was the practice of the Mass Standards Group and its successor, the Mechanical Metrology Group, (MechMet) to specify uncertainties associated with values of variables as one standard deviation with an assumed normal or Gaussian distribution. This statement corresponds to a confidence level of approximately 68%. With the acceptance and publication of ISO Guide to the Expression of Uncertainty in Measurement (First Edition 1993) and with the growing international consensus on the provision of uncertainties with confidence levels of approximately 95%, this practice has changed accordingly. Unless otherwise explicitly stated, the uncertainties provided in calibration reports issued by MechMet shall correspond to a confidence level of approximately 95%. All such reports will bear a statement such as the following: Uncertainties specified in this report are expanded uncertainties representing a confidence level of approximately 95% obtained by multiplying the combined standar
