Metrologically traceable calibrations can be obtained from the NMI whose service is suitable for the intended need and is covered by the CIPM MRA or an accredited calibration laboratory whose service is suitable for the intended need and the Accreditation Body is covered by the ILAC Arrangement or by Regional Arrangements recognised by ILAC. The trace can also be transferred inside the company from reference standards to the equipment used.
At its most simple, calibration as a term means the comparison of what is indicated by the measuring device against a more precise measure, e.g. measurement standard. The result of this is the measuring device's error that can be corrected with a correction factor or by adjustment. On the other hand, calibration provides information on the status of the device.
In addition to measuring devices, calibration can be performed on measuring systems, material measures or reference materials.
Calibrations are always also related to measurement uncertainty that describes the reliability of the measurement. Each calibration of the traceable comparison chain increases measurement uncertainty in the result. In other words, the further away from the realisation of the SI system the result is, the greater the measurement uncertainty of the measuring result.