NOTE 1 A calibration may be expressed by a statement, calibration function, calibration diagram, calibration curve, or calibration table. In some cases, it may consist of an additive or multiplicative correction of the indication with associated measurement uncertainty.

NOTE 2 Calibration should not be confused with adjustment of a measuring system, often mistakenly called “self-calibration”, nor with verification of calibration.

NOTE 3 Often, the first step alone in the above definition is perceived as being calibration.

ANNOTATION (informative) [4 September 2015] The VIM3 definition of calibration extends the previous (VIM2) one-step definition. For practical reasons a second operational step is introduced in order to facilitate assigning a measured value and measurement uncertainty to an item being measured by the calibrated measuring instrument. In the past this second step was usually considered to occur after the calibration. Both steps together facilitate in a practical way the demonstration of metrological traceability of measurement results (measured values and associated measurement uncertainty) obtained when using the measuring instrument after it has been calibrated.

ANNOTATION (informative) [4 September 2015] Calibration should not be confused with verification or adjustment. Calibration is a prerequisite for verification, which provides confirmation that specified requirements (often maximum permissible errors) are met. Calibration is also a prerequisite for adjustment, which is the set of operations carried out on a measuring system such that the system provides prescribed indications corresponding to given values of quantities to be measured, typically obtained from measurement standards.