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However, many countries also regulate Health and Safety policy and
evidential measurements. Legal metrology covers measurements and
measuring instruments that the state considers to be to much a
sensitive subject for society. The Technical Barriers to Trade
Agreement (World Trade Organization) sets up a framework under
which technical regulations may be developed, and this framework
applies to the scope of legal metrology. Article 2.2 defines what is and
is not be covered by legal metrology:
Article 2.2
(...) technical regulations shall not be more trade-restrictive than
necessary to fulfill a legitimate objective.
(...) legitimate objectives are inter alia: national security requirements,
the prevention of deceptive practices, protection of human health or
safety, animal or plant life or health, or the environment.
The first aim of legal metrology is to define which units of
measurement are acceptable in the relevant country and for what
purposes. In most countries, legal units are the SI units, plus special
units for specific applications and, in some countries, customary units.
In relation to measurements, legal metrology regulations may require
that certain measurements be carried out, that transactions be based on
these measurement results and it may require minimal performance
levels for these measurements. It is however quite unusual for
regulations to prescribe the maximum uncertainty of such regulated
measurements as defined by the Guide to the Expression of
Uncertainty in Measurement (GUM) Regulations on measurement
results, which generally consist of:
– setting acceptable limits to the content of prepackages compared
with their nominal value,
– prescribing that measurements shall be performed with instruments
of a given accuracy class subject to legal control.
The third part of legal metrology consists of submitting certain
categories of measuring instruments to legal control. Depending on
the country, this regulatory scope may be limited to a few categories
used in domestic trade (weighing scales, petrol pumps, etc.), or may
cover categories of instruments used for transactions between
companies. Most often the instruments used for levying taxes are the
object of special attention from the regulatory authorities. Usually, the
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