Appendices
Glossary
D
D-9
specifications
A precise statement of the set of requirements satisfied by a measurement system or
device.
stability
A measure of the freedom from drift in value over time and over changes in other
variables such as temperature. Note that stability is not the same as uncertainty.
standard
A device that is used as an exact value for reference and comparison.
standard cell
A primary cell that serves as a standard of voltage. The term “standard cell” often refers
to a “Weston normal cell”, which is a wet cell with a mercury anode, a cadmium mercury
amalgam cathode, and a cadmium sulfate solution as the electrolyte.
systematic errors
Errors in repeated measurement results that remain constant or vary in a predictable way.
temperature coefficient
A factor per °C deviation from a nominal value or range that the uncertainty of an
instrument increases. This specification is necessary to account for the thermal
coefficients in a calibrator’s analog circuitry.
test uncertainty ratio
The numerical ratio of the uncertainty of the measurement system or device being
calibrated to the uncertainty of the measurement system or device used as the calibrator.
(Also called “test accuracy ratio.”)
thermal emf
The voltage generated when two dissimilar metals joined together are heated.
traceability
The ability to relate individual measurement results to national standards or nationally
accepted measurement systems through an unbroken chain of comparisons, i.e., a
calibration “audit trail.”
Measurements, measurement systems or devices have traceability to the designated
standards if and only if scientifically rigorous evidence is produced on a continuing basis
to show that the measurement process is producing measurement results for which the
total measurement uncertainty relative to national or other designated standards is
qualified.
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