International Legal Metrology Documentary Standards

The International Organization of Legal Metrology (OIML)

OIML is the international organization for developing documentary standards related to regulated and legally mandated measurements. OIML is an inter-governmental treaty organization established in 1955 by the “Convention” (the treaty), which has an objective of harmonization of national regulations and metrological controls (e.g., type approval, verification, etc) applied by legal metrology authorities. There are 60 Member States (voting) and 68 Corresponding Members (nonvoting). The oversight body of OIML is the International Committee of Legal Metrology (CIML), which meets annually. Each Member State has one CIML Member. A meeting of the OIML Conference is held every four years to establish general policy, vote on the budget and confirm the decisions of the CIML. The United States ratified the Convention and joined OIML in 1972.

The OIML utilizes Technical Committees (TCs), Subcommittees (SCs), and Project Groups (PGs) comprised of representatives from member countries to develop model regulations and standards. In OIML, the standards are referred to as Recommendations. International consensus in the legal metrology community is reached through TC, SC and PG activities. The composition of the TCs SCs and PGs includes representatives from Member States and liaison representation from international standardization and technical organizations, manufacturers’ associations and regional regulatory bodies. Under the coordination of a Secretariat or a Convener, experts establish international technical guidelines for the metrological performance and testing procedures of measuring instruments subject to legal controls. The TCs are organized by general measurement discipline and the SCs are assigned specific types of measuring instruments or areas for standards development. The PGs focus on individual projects and are disbanded after completing their mission.

During development, Recommendations go through successive incomplete drafts designated as 1 WD (Working Draft), 2 WD, etc. When a TC, SC or PG addresses all necessary elements in a Recommendation the designation shifts from a WD to a Committee Draft (CD) with successive drafts numbered 1CD, 2 CD, etc. Following a successful TC, SC or PG ballot and approval, a CD is designated as a Draft Document (DD) or a Draft Recommendation (DR) and sent to the International Bureau of Legal Metrology (BIML) for approval by the CIML. The BIML provides the administrative, technical and editorial staffing function for the OIML. Following CIML approval, the BIML publishes and provides for free distribution of the Documents and Recommendations through the OIML website.

The OIML has developed a Certificate System for measuring instruments that comply with the Recommendations to promote global regulatory-body acceptance of test reports, thereby avoiding duplicative type evaluation testing requirements. Manufacturers may submit instruments to testing facilities authorized by national Issuing Authorities, which are designated by their CIML Members. The OIML web site database lists the Issuing Authorities and the OIML Certificates of Conformity (CC) submitted by the various national Issuing Authorities for registration by the BIML.

The OIML has developed a Mutual Acceptance Arrangement (MAA) that is related to the OIML Certification system used for Type Evaluations. The goal of the MAA is for the participants to accept and utilize Test Reports validated by an OIML MAA Certificate of Conformity. The scheme designates Participants in the MAA as either Issuing Participants (IPs) or Utilizing Participants (UPs). Issuing Authorities that will issue and use OIML MAA Certificates of Conformity are designated as IPs. Tests reports associated with these OIML MAA Certificates will also be accepted and utilized by UPs to issue, for example, national type approvals. To foster confidence, the MAA includes an evaluation of the competence and testing capabilities of the Testing Laboratories of OIML Issuing Authorities applying to be an IP, according to the international standard ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories. This evaluation may be carried out either by accreditation or by peer assessment. The Committee on Participation Review (CPR), comprised of experts from participating countries, studies the application files of potential participants and decides on the need to conduct peer assessments, considering the accreditation of the Testing Laboratories and the scope of these accreditations. Evaluation reports are distributed to the participants, and when all participants agree on the acceptability of the IP applicants, the IP applicants are allowed to sign the Declaration of Mutual Confidence (DoMC). The MAA covers OIML R 60 (Load cells), OIML R 76 (Nonautomatic weighing instruments), and OIML R49 (Water meters). The National Conference on Weights and Measures (NCWM) signed the DoMC (as a Utilizing Participant) for R60. Consequently, the U.S. National Type Evaluation Program (NTEP) accepts test data on load cells that are tested according to the requirements in OIML R60 (and additional, agreed-upon requirements), from Issuing Participants under the DoMC, to use as the basis of issuing NTEP Certificates. Over 30 such NTEP Certificates have been issued.