To ensure fair trade and to protect consumers from being deceived by inaccurate measurements the mandatory control of measuring instruments through verification has been impose by the governs across the centuries. It is considered the vulnerability of the consumer in the market in many consumers defense codes, which prescribe the govern action aiming effectively to protect the consumer assuring products and services with adequate standards of quality, security, durability and performance.

The legal metrology service, in Brasil a competence of Inmetro, takes this vulnerability into account but also has the commitment of being independent and impartial in the execution of its public duties not having economic self-interest so that parties concerned the measurement result are satisfied.

The International Vocabulary of Terms in Legal Metrology (VIML) defines the legal metrology as being:

"part of metrology relating to activities which results from statutory requirements and concern measurement, units measurement, measuring instruments and methods of measurement and which are performed by competent bodies"

To ensure the credibility of measurement result in legal metrology are necessary the regulations, the technical means and the operational processes.

Purposes for Legal Metrology:

• to protect the consumer when he or she purchases measurable goods and services and to provide the prerequisites for reliable measurements in commercial transactions in the interest of fair trade,
  
• to ensure reliability of measurement in health, labors and environmental protection and in similar areas of public interest, and
• to strengthen confidence in official measurements.
  

• consumer protection,
• level playing field for commercial transaction,
• effective store control,
• reduction of complains and cost of the transactions,
• frauds control,
• full benefits to national product exportation,
• full collection of government's taxes.

• objective and field of application
• terminology
• units of measurement
• metrological and technical requirements
• marking of an instrument
• metrological control
• testing procedures
  

The metrological requirements specify some performance tests and the maximum permissible errors to a given instrument's accuracy class, under nominal operational conditions, influence factors (influence of quantities and time) and disturbances (ex. electromagnetic compatibility). The accuracy of the used verification standards should be also specified, commonly it is applied the 1/3 proportion in the accuracy levels of legal metrology reference standards.

The technical requirements are aiming at preventing functional and operational fails and not facilitating manipulations or frauds. The indication and/or printing of a measuring result shall be clear and unambiguous.

Legal Metrological Control

The Legal Metrological Control [VIML 2.1] has the following operational processes or activities:

• legal control of measuring instruments,
• metrological supervision, and
• metrological expertise.

The Legal Control of Measuring Instrument may subject the instruments to the following operations of preventive nature:

• type approval,
• initial verification of new measuring instrument,
• periodical verification of instruments in use,
• after repair verification of instruments in use,
• maintenance of measuring instruments,
• participation in comparison measurements.

The Metrological Supervision [VIML 2.3] The Metrological Supervision [VIML 2.3]

"Control exercised in respect of the manufacture, import, installation, use, maintenance and repair of measuring instruments, performed in order to check that they are used correctly as regards the observance of metrological laws and regulations". It includes checking the correctness of the quantities indicated on and contained in prepackages.

The Metrological Supervision may need investigation with inspection carried out on-spot in conditions in situ that is normally performed at manufacturers and repairs of measuring instruments, at users of measuring instruments and at manufacturers or importers of prepackages products or, carried out ex-situ in the laboratory of a competent body. Legal actions are to be taking in case of any violation found in the supervision. In many cases the supervision is made joint the normal operations of the legal control of a measuring instrument for economical efficiency.

The Metrological Expertise [VIML 2.4]

"All the operations for the purpose of examining and demonstrating, e.g. to testify in a court, the condition of a measuring instrument and to determine its metrological properties, among others by reference to the relevant statutory requirements".

International relationship

Inmetro also collaborates for the uniformity of Legal Metrology activities application in the world, for its active participation in the Mercosul and the OIML - International Organization of Legal Metrology.