Calibration is defined as a test during which known values of measurand are applied to the nsducer and corresponding output readings are recorded under specified conditions. The definition includes the capability to adjust the instrument to zero and to set the desired span. An interpretation of the definition would say that a calibration is a comparison of measuring equipment against a standard instrument of higher accuracy to detect, correlate, adjust, rectify and document the accuracy of the instrument being compared.Typically, calibration of an instrument is checked at several points throughout the calibration range of the instrument. The calibration range is defined as the region between the limits within which a quantity is measured, received or transmitted, expressed by stating the lower.

Calibration Certificates must contain specific information to be considered in compliance with ISO / IEC 17025 : 2017 requirements. This standard identifies the information that must be provided on every calibration certificate. The information is necessary for the interpretation of the test results, traceability to NPL, and documentation of requirements being met as may be required by the method used.