Metrology Terms

Accuracy


Accuracy
closeness of a test result to an accepted reference value; trueness and precision (ISO5725-1)

Trueness
closeness of average value to an accepted reference value, normally expressed in terms of bias (ISO5725-1)

Bias of a measurement method
difference between expected test results from all labs using that method and accepted reference value (ISO5725-1)

Lab bias
difference between expected test results from one laboratory and an accepted reference value (ISO5725-1)

Precision
closeness of independent test results (taken from repeated measurements) to each other, normally expressed as standard deviations; does not relate to the accepted true value (ISO5725-1)

Repeatability
precision under repeatability conditions (ISO5725-1)

Repeatability conditions
factors that could cause change (see below) are constant, creating minimum variability in results (ISO5725-1)

Reproducibility
precision under reproducibility conditions (ISO5725-1)

Reproducibility conditions
factors that could cause change (see below) are varied and thus contribute to the variability of test results; maximum variability in results achieved when all factors are varied (ISO5725-1) Factors that could cause changes in precision:


Quality Assurance


Calibration
set of operations which establish the relationship between values indicated by a measuring instrument, measuring system, material measure or reference material and the corresponding values of a quantity given by a reference standard (ISO10012-1)

Reference material (RM)
material or substance used for calibration of an apparatus, the assessment of a measurement method, or for assigning values to materials (ISO10012-1)

Internal reference material
RM developed by a user for his/her own internal use (ISO11095)/DD>

External reference material
RM provided by someone other than the user (ISO11095)

Certified reference material
RM issued and certified by an organization recognized as competent to do so (ISO11095)

Resolution (of an indicating device)
ability to distinguish immediately adjacent values (ISO10012-1)

Resolution (of a displaying device)
smallest difference between indications of a displaying device that can be distinguished (ISO10012-2)

Measurement standard
a material measure, measuring instrument, RM or system intended to define, conserve or reproduce one or more values of a quantity in order to transmit them to other measuring instruments by comparison (ISO10012-1)

Traceability
ability to relate the result of a measurement to international or national measurement standards, through an unbroken chain of comparisons (all having stated uncertainties) (ISO10012-1 and -2)

Uncertainty of measurement
range within which the true value of a measured quantity is estimated to lie, generally with a given likelihood (ISO10012-1)


* All of these terms can be found in the following International Standards: ISO 5725-1, ISO 10012-1, ISO 10012-2, and ISO 11095. These particular standards (as well as several others) can be viewed at the George C. Gordon Library, and their exact call numbers can be found by searching for 'International Standard' in the Library Catalogue. International Standards can be purchased individually (in paper or PDF versions, and most are available in various languages) at the ISO Online Catalogue.
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Last modified: September 13, 2007 10:36:06