According to the definition, calibration refers to procedures with which a connection can be established between the result of a measuring instrument or a measuring system or the measurement unit value represented by a material measure or reference material under specified circumstances and the corresponding values implemented with measurement standards.
Calibration is a procedure that must be performed at regular intervals. It verifies the working condition of the measuring devices used, while confirming that the laboratory is aware how much “error” there is in the measurement device's reading. In other words, calibration is a part of confirming the validity of the results. It is between the client and the customer to agree whether adjusting the measuring device to show the correct reading is a part of the commission or not.
The task of accredited calibration laboratories is to transfer traceability or to indicate the connection of the measurement result or the measurement standard used by the client to the references (usually national or international measurement standards) with the help of an unbroken chain of comparisons in which all uncertainties of comparisons in the chain have been notified. In turn, measurement uncertainty is a parameter related to the measuring result that describes the assumed variation of the measured quantity. The size of the measurement uncertainty influences the result's approval limits and is impacted on by the measuring target, measuring instrument, person performing the measurement, measuring method and environmental conditions at the time when the measurement is performed.
Accredited calibration laboratories calibrate measuring devices related to many parameters, including various electrical parameters, pressure, temperature, length, volume, mass, power and hardness.
The quality management system of an accredited calibration laboratory meet the principles of ISO 9001 standard. The international organisations ISO, ILAC and IAF have stated this compliance in their joint declaration.
Metrological traceability is one of the elements that establishes international confidence in the worldwide equivalence of measurements. The importance of metrological trafeability is stated in joint declaration made by four international bodies resposible for metrology, accreditation and standardization (BIPM, OIML, ILAC and ISO).
The SFS/EN ISO/IEC 17025:2017 standard is the accreditation requirement for calibration laboratories.
In addition, the mandatory guidebook EA-4/02 M:2013 related to the calculation and reporting of measurement uncertainty applies to accredited calibration laboratories. As one of their quality assurance procedures, calibration laboratories are expected to also take part in proficiency testing. FINAS Assessment Principle FINAS Assessment Principle A2 states the principles for assessment of the quality assurance and proficiency testing practices in laboratories.
Accredited calibration laboratories use the FINAS accreditation symbol in which the identification number of the accredited body is of the form KXXX.