The tiered structure through which a unit is passed down: primary standards at a national metrology institute, then reference standards held by accredited calibration labs, then working standards used for routine calibration, and finally the shop and process instruments that measure product. Uncertainty grows at each level, so a gauge at the bottom always carries more than the standard at the top. Labs usually draw it as a pyramid in their quality manual.
Our 10 volt Zener sits at the top of our calibration hierarchy, everything on the bench traces through it.
Also heard as
- traceability pyramid
- metrology pyramid
Do not mix it up with
- Traceability chain: The chain is the specific path for one result; the hierarchy is the general ladder of standard levels.
Related terms
Traceability chain
The documented sequence of calibrations linking a working instrument back to national or SI-level standards.
Primary standard
A standard that gets its value straight from the unit definition, not from calibration against another standard.
Reference standard
A lab's highest-level standard for a quantity, used only to calibrate other standards and never for routine work.
Working standard
A standard used routinely to calibrate instruments, itself checked against the lab's reference standard.
NMI
National metrology institute, the body that realizes a country's measurement units at the top of its traceability chain.