Calibration services
Definitions

Calibrate, adjust, verify or legally verify?

What does "calibration" actually mean?

Calibration is the act of determining and documenting, in a traceable manner, the deviations between a measuring instrument called device under test (DUT) and a reference device called reference standard.

The result of this comparison shows the measuring deviations at different measurement points and can be provided in absolute or relative form. The regular calibration of measurement instruments ensures the precision and reproducibility of the measurement data. The reference measurement is made with a reference device.

Traceability refers to the uninterrupted chain of comparative measurements related to the measuring results of a measuring instrument and the specific, higher-ranking national standard.

The resulting hierarchy is based on accreditation, i.e. the calibrating authorities have been assessed for their technical competence and thus formally recognized. The highest-ranking national authorities for metrology are the Physikalisch-Technische Bundesanstalt (PTB) in Germany and the National Institute of Standards and Technology (NIST) in the USA. These bodies provide reference standards of the highest accuracy, such as the standard meter or standard foot, for all physical and legally required quantities for use in calibration.

What is meant by "adjustment"?

As opposed to calibration, adjustment is the act of setting a measuring instrument to a measurement deviation that is reduced as much as possible in order for the deviations to stay within the limits of error. Thus, adjustment requires an intervention on the measuring instrument, which usually results in permanent changes to the device.

What is "verification"?

Verification is about providing objective proof that a measuring instrument meets specific requirements.

As opposed to calibration, uncertainty of measurement is not indicated, only a pass or fail statement is made. Verification can cover secondary measurands such as the sensor, the transducer or I/O modules via test signals.

What is meant by "legal verification"?

Legal verification means performing legally required checks of measuring instruments, e.g. scales used in food retailing, that are subject to public interest and are used to set prices. Standardization is performed by specific authorities and is thus governed by severe regulations.

Measuring and testing technology in comparison
	Calibration	Adjustment	Verification	Legal verification
Certificate with accuracy	Yes, documents the deviation from the data sheet specification			Yes, by an accredited certification body
Measurement uncertainty documented	Yes, including information on traceability	No, as there is no documentation	No, only qualitative statement on functionality	Yes, within legally prescribed tolerances
Traceability to standards	Yes, to national or international standards	Possible through subsequent calibration	Possible if reference device is traceable	Yes, certified by the state
Typical measuring instruments	Sensors, scales, pressure/temperature measuring devices	Sensors, laboratory equipment, production machines	Test devices, sensors	Scales, petrol pumps, measuring instruments used for billing purposes (gas/water/electricity)
Typical application	Quality assurance in industrial environments, laboratories (pharmaceuticals, food, automotive)	Optimisation of measurement accuracy in production and development	Quick check in production or in the incoming goods department	Measurement technology used for trade and billing (e.g. scales, petrol pumps)
Required according to standard	ISO 9001, IFS, GMP, HACCP, ISO/TS 16949, ISO 50001 etc.	Not required, but often necessary for compliance with specifications	Depending on the respective standard (e.g. ISO 10012)	Regulated by law for measuring instruments subject to legal verification
Audit-compliant	Yes, calibration certificate serves as proof	No, only through subsequent calibration	Partially, depending on standard requirements	Yes, verification mark or official certificate are recognised forms of proof
Executing service provider	Accredited and non-accredited calibration laboratories	Manufacturers, maintenance service providers, service technicians	Internal quality assurance or external certification bodies	Measurement offices or accredited certification bodies
Advantages	Objective assessment of the measurement deviation, traceability, basis for quality assurance	Optimisation of measurement accuracy	Quick check with little effort	Legally recognised, required for billing-related measurements
Particularities	Only shows the deviation - no interference with the device	Recalibration is necessary after each adjustment	Check only, no interference with the device	Required by law for certain use cases
Costs (approximate)	– (depending on required accuracy and calibration standard)	(depending on the type and complexity of the adjustment)	– (low to medium, depending on testing effort)	(statutory testing fees)