What should I do if the calibration uncertainty of my measurement standard is greater than ¼ of the MPE of the measuring instrument that I want to verify?

In some technical fields, the performance of the references is sometimes limited in comparison with the MPEs of the instruments to be verified. In this case, you can either look for references with smaller uncertainty, or proceed with the verification anyway, bearing in mind that the conformity zone will be very small. The zone of conformity is the remaining zone, after the tolerance zone (MPE) of the measurement uncertainty has been reduced. For more information, refer to FD X 07-022 or the guide ILAC G8: 03/2009 “Guidelines on the Reporting of Compliance with Specification”, which can be downloaded on the ILAC site at http://www.ilac.org/guidanceseries.html