In verification, which statement about a standard used for regular checks (working reference standard) is true?

• A. The same as the ultimate master standard.
• B. A standard used for occasional checks with no uncertainty.
• C. A standard used for regular verification checks; not the ultimate master.
• D. An environmental reference standard.

Answer: (C)

A working reference standard is the reference kept specifically for routine verification checks to confirm an instrument stays within specification between formal calibrations. It provides a practical, readily available check of performance, while the ultimate master standard remains the highest-accuracy reference used to establish traceability and calibrate other standards. It is not an environmental reference standard, which is used for monitoring environmental conditions rather than instrument performance, and it does carry measurement uncertainty (there isn’t a zero-uncertainty check). So, using a standard for regular verification checks and not treating it as the ultimate master is the correct concept.