Calibration Glossary

Calibration Terminology

The field of calibration has a huge vocabulary describing the methods and processes used to verify the measurement accuracy of masters, gages and other measuring instruments. The following definitions are for the most commonly used terms.


A2LA are the initials of American Association for Laboratory Accreditation, a non-profit accrediting agency specializing in the accreditation of calibration and testing laboratories.

Accreditation is a process used by a qualified independent agency to verify the quality system and technical capability of a calibration laboratory to a recognized standard such as ISO 17025.

Accuracy defines how close a measured value is to the true value of the dimension.

Calibration is the set of operations which establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material and the corresponding values realized by standards.

Calibration Certificate or Report is the document that presents calibration results and other information relevant to a calibration.

Calibration Frequency is the time intervals at which instruments, gages and masters are calibrated. These intervals are determined by their user based on the conditions of their use to ensure their performance or size remain within acceptable limits.

Calibration Limits is a tolerance applied to gages and instruments beyond which they are not considered suitable for use.

International (Measurement) Standard is a standard recognized by an international agreement to serve internationally as the basis for fixing the value of all other standard of the quantity concerned.

Limits of Permissible Error (of a measuring instrument) are the extreme values of an error permitted by specifications, regulations, etc. for a given measuring instrument.

Measurement Assurance is the technique that may include, but is not limited to: 1) use of good experimental design principles so the entire measurement process, its components, and relevant influence factors can be well characterized, monitored and controlled; 2) complete experimental characterization of the measurement process uncertainty including statistical variations, contributions from all known or suspected influence factors, imported uncertainties, and the propagation of uncertainties throughout the measurement process; and 3) continuously monitoring the performance and state of statistical control of the measurement process with proven statistical process control techniques including the measurement of well characterized check standards along with the normal workload and the use of appropriate control charts.

Measuring and Test Equipment includes all of the measuring instruments, measurement standards, reference materials, and auxiliary apparatus that are necessary to perform a measurement. This term includes measuring equipment used in the course of testing and inspection, as well as that used in calibration.

Quality System is the organizational structure, responsibilities, procedures, processes and resources for implementing quality management.

Resolution represents the smallest reading unit provided by an instrument.

Traceability is the path by which a measurement can be traced back to the source from which it is derived, such as NIST in the United States. Direct traceability implies that the laboratory has its primary masters calibrated directly by such an agency for reduced measurement uncertainty.

Uncertainty of Measurement is a parameter associated with the result of a measurement that characterizes the dispersion of the values that could reasonably be attributed to the measurand.