It is often the practice of Calibration/Metrology professionals to report data to the last digit, however, it is not always the best method. Writing extranious digits leads to transcription errors. It is customary to report the Standards indication to one decade greater than the item being...
edpaq,
ISO-10012 has in essence been replaced with ISO-17025. However, your question can be best understood with a good read of ISO Guide-25. "Guide for Measurement Uncertainty" (or affectionaltely known as "The GUM).
Basically you need to account for all significant sources of error. You need...