National accreditation body appointed by the Italian government.


Process through which the national accreditation body assesses a body suitable for issuing a service according to a specific standard. In the case of Calibration Laboratories, the Accreditation Body (ACCREDIA) assesses the Centre (CAB -  Conformity Assessment Body) competent and impartial according to the requirements of the UNI CEI EN ISO/IEC 17025:2018 Standard.

Accreditation body

National body in charge of the assessment and accreditation of Laboratories and Certification Bodies. According to the EU law 765/2008 it has to be a single body for each EU country. National Accreditation Bodies are mutually recognised worldwide through ILAC MRA agreements.


Characteristic of an instrument that provides an indication of its maximum permissible error by means of a value, percentage or class.


Operation of mechanical or electronic adjustment of the instrument to reduce systematic error.


Process of characterisation of a measuring instrument which results in the measurement error of the instrument and the associated uncertainty of calibration.

Calibration certificate

Document reporting the results of the calibration. The document must include the customer's personal data, the instrument's personal data, relevant information on the conditions, methods and traceability of the calibration, the measurements accompanied by the relative measurement uncertainty. The accredited Calibration Certificate guarantees the traceability of the measurements and can be used to transfer the traceability within the organisation using it. An accredited calibration certificate is also sufficient to demonstrate the competence and impartiality of the issuing laboratory, which is necessarily accredited according to ISO/IEC 17025. Those who rely on an accredited calibration do not need any further assessment of the calibration provider to comply with the requirements of ISO 9001.

Calibration Report

A document reporting the results of calibration. A Laboratory issuing it does not require an accreditation and doesn't need to conform to the requirements of any standard. Because of this, it is not a document considered valid for the purposes of satisfying the requirements of certified Management Systems. In particular, it does not guarantee traceability to national and international standards.

Furthermore, it does not guarantee the competence of the organisation that issues it, and obliges the end user to carry out an assessment of the supplier of the calibration report.

Certificate of accreditation

In the field of Calibration Laboratories, a document issued by the Accreditation Body certifying the quantities and fields for which the Laboratory is accredited and the period of validity of the same. The measurement capabilities of the laboratory are also specified for each accredited sector, generally by means of an annex to the Certificate of Accreditation which contains the CMC (Centre Measurement Capability), i.e. the best uncertainties of the centre.

Confidence level

A percentage value indicating the probability that the range defined by the measurement uncertainty includes the true value.


Value to be added to the instrument reading to compensate for its systematic error. It is intended as the opposite of error.


Deviation over time of the value indicated by an instrument. It may be due to changed physical conditions caused by wear over time. Defined as the difference between the error values found in two consequential calibrations.


Acronym for National Institute of Metrological Research. It is the Italian National Metrological Institute. Through it, reference instruments are maintained and metrological traceability is disseminated to the Calibration Centres.

Measurement error

Difference between the reading of the instrument under calibration and the reference value of the quantity to be measured. It is an estimate of the systematic error of the instrument.

Measurement uncertainty

Value indicating the dispersion of the possible true values of the measurement.

It is calculated from the combined uncertainty u, which is obtained by taking into account all uncertainty components that have influence in that particular measurement. Calibrations are presented with the expanded uncertainty value U, which is calculated by multiplying the combined uncertainty by a parameter k adequate to ensure a predefined level of confidence.

On the ISO 17025 calibration certificate, the value k=2 is used to achieve a 95% confidence level.


Metrology is the science of measurement and its application (from VIM - International vocabulary of metrology).


Property of an instrument to measure a quantity in a repeatable manner in the short term. It is an estimate of the random error of the instrument.

Reference standard

Measurement instrument through which the laboratory disseminates metrological traceability to its internal instruments. It is calibrated externally by a National Metrological Institute or an accredited Calibration Centre.


Property of a calibration that ensures that measurements are consistent with the International System and comparable to measurements made in any other laboratory in the world. Traceability is guaranteed if all instruments used for calibration have undergone accredited calibrations. At the same time, the calibration of these reference instruments must also be carried out by comparison with instruments that meet this requirement. This establishes a direct relationship with national and international standards.

Accreditation of the laboratory carrying out the calibration is essential to ensure the traceability of the measurements.


International Vocabulary of Metrology. English version JCGM 200:2012, downloadable free of charge from the BIPM website.

Working standard

A measuring instrument used to disseminate metrological traceability to devices under calibration. It is calibrated internally for comparison with a Reference Instrument.