The uncertainty component taken from the calibration of the reference standard or instrument used to make a measurement, typically read off its certificate as an expanded uncertainty and divided by the stated coverage factor. It is the link that carries uncertainty down the traceability chain, so no lab can claim a smaller uncertainty than the one it imports. Drift of the standard since that calibration belongs on a separate budget line.
Imported uncertainty from the NMI cert is already 0.5 ppm, so a 0.3 ppm CMC claim can't be right.
Also heard as
- reference standard uncertainty
- uncertainty of the standard
Related terms
Uncertainty budget
A table listing every uncertainty source in a measurement with its size, distribution, divisor and contribution to the total.
Traceability chain
The documented sequence of calibrations linking a working instrument back to national or SI-level standards.
Reference standard
A lab's highest-level standard for a quantity, used only to calibrate other standards and never for routine work.
Calibration certificate
The document reporting a calibration's results, uncertainties, conditions and traceability for one specific item.
Drift
Gradual change in an instrument's readings over time that comes from the instrument itself, not from what it measures.