What is the difference between MID 2014/32/EU and NAWI 2014/31/EU?

MID (Measuring Instruments Directive) covers ten categories of measuring instruments defined in Article 2(1) and detailed in the instrument-specific Annexes III to XII, numbered MI-001 to MI-010: water meters, gas meters, active-energy electrical meters, heat meters, fuel dispensers, automatic weighing instruments, taximeters, material measures, dimensional measuring instruments, and exhaust-gas analysers. NAWI (Non-Automatic Weighing Instruments) covers only non-automatic weighing instruments, that is, those requiring operator intervention during weighing (shop scales, laboratory balances used for trade). Both directives are parallel, of the same date, aligned on Decision 768/2008/EC.

Which instruments fall under MID and which do not?

Two conditions combine. The instrument must belong to one of the ten categories of Annexes III to XII, and the Member State where it is used must have chosen to regulate that measuring task: Article 3 makes the MID optional, each Member State deciding whether to prescribe the use of regulated instruments for reasons such as consumer protection, fair trading or taxation, and explaining its reasons when it does not. A water meter billed by a distributor in a country that regulates water metering needs MID conformity; the same device used only for internal monitoring does not.

What is Maximum Permissible Error (MPE) and accuracy class?

The Maximum Permissible Error (MPE) is the maximum allowed deviation between the indicated value and the true value, expressed as a percentage or as an absolute value depending on the category. The accuracy class groups instruments by applicable MPE level. The exact values are set by the instrument-specific annex (MI-001 for water meters, MI-002 for gas meters, and so on) and are not transferable from one category to another. The MID sets the errors that apply when the instrument is assessed and placed on the market; errors allowed in service, and the frequency of in-service verification, are set by national rules.

What is the format of the M marking and what does it certify?

A MID-compliant instrument carries two combined markings: the classic CE marking and the supplementary metrology marking, consisting of the capital letter "M" and the last two digits of the year of affixing, surrounded by a rectangle. The rectangle is the same height as the CE marking, and the M marking immediately follows the CE marking (Articles 21 and 22). They are followed by the identification number of the notified body where that body is involved in the production control phase (for example "CE M26 0123"). The absence of the M marking on an instrument that falls under MID is a serious non-conformity: an instrument sold with the CE marking only cannot be used for legal-metrology purposes. The M marking attests specific conformity to MID requirements.

Which conformity assessment modules are allowed under MID?

MID lists, in its Annex II, the authorised modules within the 768/2008/EC framework. The most frequent combinations are B+D (EU-type examination plus production quality assurance), B+F (examination plus product verification), H1 (full quality assurance with design examination) and G (unit verification). Each annex MI-001 to MI-010 lists the modules the manufacturer can choose from. A notified body is involved in almost every route; the one exception is module A2 (internal production control with supervised checks at random intervals), available only for capacity serving measures under MI-008.

What does WELMEC 7.2 say about embedded software in measuring instruments?

WELMEC 7.2 is the consolidated European guide on software in measuring instruments. Published by WELMEC (European Cooperation in Legal Metrology), it describes the requirements applicable to embedded, separate and downloaded software to ensure stability of the metrology functions, data integrity, traceability of updates, and separation between legally relevant and non-legally relevant functions. Notified Bodies rely on WELMEC 7.2 to assess software documentation. A MID instrument whose software does not follow the WELMEC 7.2 doctrine is rarely certified.

What is the link between MID and OIML recommendations?

OIML (International Organisation of Legal Metrology) publishes international recommendations (the "OIML R" series) that serve as the technical foundation for most national legal-metrology regulations, including MID. Each MI-00x category references at least one OIML recommendation: R 49 for water meters, R 137 for gas meters, R 46 for active-energy meters, R 75 for heat meters, R 117 for fuel dispensers, R 51 and R 61 for automatic weighing instruments, R 21 for taximeters. The MID gives OIML documents a role no other New Legislative Framework directive has: under Article 14(2), conformity with parts of normative documents whose list is published in the Official Journal gives presumption of conformity, just like a harmonised standard. OIML certificates themselves do not replace the EU conformity assessment.

Do smart meters fall under MID?

Yes. A communicating active-energy electrical smart meter falls under MID category MI-003 for its metrology functions, and remains subject to other European directives for its non-metrological functions: RED 2014/53/EU for the radio part, EMC 2014/30/EU for electromagnetic compatibility, GDPR for personal consumption data, and the Cyber Resilience Act for product cybersecurity (reporting obligations from 11 September 2026, full requirements from 11 December 2027). MID covers metrology stability and energy-counting integrity; it does not cover data privacy or cybersecurity.

MID 2014/32/EU: Measuring Instruments (MI-001 to 010)

Hugues Orgitello updated 7 Oct 2026 16 min read

Directive 2014/32/EU, known as MID (Measuring Instruments Directive), governs measuring instruments used for legal-metrology purposes in the European Union: commercial transactions, public-interest measurements, fiscal and customs declarations, occupational health and safety. It replaced Directive 2004/22/EC to align with the New Legislative Framework. Two features set it apart from the other CE directives: it is optional, each Member State deciding which measuring tasks to regulate (Article 3), and it lets international OIML normative documents give presumption of conformity alongside harmonised standards (Article 14). Article 2(1) of the directive enumerates ten categories of instruments covered, detailed in the instrument-specific Annexes III to XII and numbered MI-001 to MI-010, ranging from water meters to exhaust-gas analysers. This page sets out the scope, the essential requirements, the categories, the authorised assessment modules, the M metrology marking, and the articulation with WELMEC, OIML and the NAWI sister directive.

The scope of legal metrology

Legal metrology covers measurement activities subject to a regulatory framework because their results carry legal or financial weight. Directive 2014/32/EU formalises four domains:

Commercial transactions: billing of the end consumer or between operators, supermarket cashier scale, domestic water or gas meter, fuel dispenser at a service station.
Public-interest measurements: protection of public health, environment and safety, air-quality or emissions monitoring, control of water for human consumption.
Fiscal or customs measurements: declaration of volumes or masses for the calculation of taxes, customs duties, and excise.
Occupational health and safety measurements: measuring equipment mandated by labour regulation (for example exposure measurements).

These are the reasons a Member State can invoke. Article 3 makes the directive optional: each Member State may prescribe the use of regulated instruments for a measuring task "where they consider it justified" for public interest, public health, public safety, public order, environmental protection, consumer protection, taxes and duties or fair trading, and must communicate its reasons to the Commission and the other Member States when it does not. The same water meter can therefore need MID conformity in one country and not in another. Even a Member State that does not regulate a task keeps the right to notify a body for it (Article 23(2)).

The directive does not apply to instruments used for internal control with no legal effect on third parties. An energy meter installed by a company to track its own consumption, without third-party billing or regulatory declaration, is outside scope. This "own use" versus "legally relevant use" distinction is decisive: it triggers the applicability of MID and the obligation of a Notified Body.

The ten instrument categories (Annexes III to XII)

Article 2(1) of the directive enumerates the ten categories of instruments covered, each detailed in a specific annex (Annexes III to XII, designated MI-001 to MI-010) that sets the specific requirements, the rated operating conditions, the maximum permissible errors, the relevant accuracy classes and the authorised conformity assessment modules.

Synoptic table of MI categories

MI annex	Category	Examples of instruments	Reference OIML recommendation
MI-001	Water meters	Domestic and industrial cold and hot water meters	OIML R 49
MI-002	Gas meters and volume conversion devices	Residential, commercial and industrial gas meters, PTZ converters	OIML R 137, OIML R 140
MI-003	Active-energy electrical meters	Standard and smart electrical meters	OIML R 46
MI-004	Heat meters	Heat meters, cooling meters, calorimeters	OIML R 75
MI-005	Continuous and dynamic measuring systems for quantities of liquids other than water	Fuel dispensers, petroleum-product metering, liquid chemical-product metering	OIML R 117
MI-006	Automatic weighing instruments	Catchweighers, gravimetric fillers, rail weighbridges, automatic weighbridges	OIML R 51, R 61, R 106, R 107
MI-007	Taximeters	Taximeters associated with motion-signal sensors	OIML R 21
MI-008	Material measures	Length material measures, capacity-serving measures (standardised wine glasses, jugs)	OIML R 138 and others
MI-009	Dimensional measuring instruments	Multi-dimensional length measuring instruments, area measuring instruments, cable-length meters, leather-area meters	Various OIML recommendations
MI-010	Exhaust-gas analysers	Vehicle exhaust-gas analysers used in technical inspection	OIML R 99

How to read the table: each line refers to a dedicated annex within Directive 2014/32/EU. The directive does not set the same accuracy thresholds for two distinct categories; the corresponding MI-00x annex must be consulted for the exact accuracy-class and MPE values. The presence of a category in the Article 2(1) list does not exhaust the obligations: a water meter used in industrial settings must also comply with cross-cutting directives (EMC, LVD if mains-powered, RED if it transmits by radio).

The essential requirements of Annex I

Annex I of MID defines the cross-cutting essential requirements applicable to all instruments. They form the common core that the specific annexes MI-001 to MI-010 then refine.

Accuracy and maximum permissible error

The instrument must maintain its accuracy under the rated operating conditions specified by the directive and the specific annexes. The directive distinguishes:

The maximum permissible error (MPE): the largest deviation allowed between indication and true value, under rated operating conditions and, where the annex says so, without disturbance or under disturbance (critical change values).
The accuracy class: a group of instruments sharing the same MPE and rated operating conditions.
In-service errors and verification: not set by the MID. Member States that regulate a measuring task set them nationally, together with the frequency of subsequent verification.

The exact values are not set by the general Annex I: they are set instrument by instrument in the MI-001 to MI-010 annexes and in the referenced OIML recommendations. Any specific MPE figure must be supported by the MI-specific annex.

Reproducibility, repeatability, sensitivity and resolution

The instrument must provide results that are reproducible over time, repeatable for a given measurement, sensitive to significant variations of the measured quantity, and with a resolution sufficient for the declared accuracy class. These notions are defined by the international vocabulary of metrology (VIM, IEC 60050-300 and JCGM 200).

Influence of external factors

Annex I requires the control of four families of influence factors on metrology performance:

Climatic factors: the manufacturer picks an upper temperature limit (30, 40, 55 or 70 °C) and a lower limit (5, −10, −25 or −40 °C) from Table 1 of Annex I, unless the instrument annex says otherwise, and declares condensing or non-condensing humidity and open or closed location.
Mechanical factors: classes M1 (low vibration and shock, light structures), M2 (significant vibration, near machines or traffic) and M3 (high vibration, mounted directly on machines or conveyors).
Electromagnetic factors: classes E1 (residential, commercial and light industrial), E2 (industrial) and E3 (vehicles).
Supply-related factors: voltage, frequency, harmonics, micro-interruptions for mains-powered instruments; voltage, current, durability for battery-powered instruments.

Conformity assessment must demonstrate that the instrument meets MPE under all admissible combinations of these factors, not only under laboratory conditions.

Durability

The instrument must keep its metrology characteristics over the typical lifetime of the category. The directive requires a long-term stability demonstration through accelerated testing or documented field experience. The instrument annexes and the referenced standards set the category-specific criteria.

Reliability and failure indication

The instrument must signal any malfunction that would take it outside the MPE, either by explicit display or by blocking the measurement function. Annex I requires that a malfunction must not result in an erroneous measurement presented as valid.

Protection against manipulation

The metrology functions must be protected against unauthorised manipulation, either by physical sealing or by software sealing (passwords, signatures, logs). It is on this point that WELMEC 7.2 elaborates the requirements applicable to software.

Documentation, markings, instructions

The technical documentation, the mandatory markings and the user instructions must allow the user and the surveillance authority to identify the instrument, its accuracy class, its rated conditions and the verification procedure.

Conformity assessment modules

MID, like all "new approach" directives revised in 2014, aligns with Decision 768/2008/EC for its assessment modules. Annex II of Directive 2014/32/EU lists the authorised modules, and each annex MI-001 to MI-010 restricts the choice to the modules relevant to the category.

Typical modules per category

Category	Authorised modules (MID Annex II)
MI-001 Water meters	B+F, B+D, H1
MI-002 Gas meters and converters	B+F, B+D, H1
MI-003 Active-energy meters	B+F, B+D, H1
MI-004 Heat meters	B+F, B+D, H1
MI-005 Fuel dispensers and liquid systems	B+F, B+D, H1, G
MI-006 Automatic weighing	Mechanical: B+D, B+E, B+F, D1, F1, G, H1. Electromechanical: B+D, B+E, B+F, G, H1. Electronic or with software: B+D, B+F, G, H1
MI-007 Taximeters	B+F, B+D, H1
MI-008 Material measures of length	F1, D1, B+D, H, G
MI-008 Capacity serving measures	A2, F1, D1, E1, B+E, B+D, H
MI-009 Dimensional measuring	Mechanical or electromechanical: F1, E1, D1, B+F, B+E, B+D, H, H1, G. Electronic or with software: B+F, B+D, H1, G
MI-010 Exhaust-gas analysers	B+F, B+D, H1

For the precise meaning of modules A, A1, B, C, D, D1, E, E1, F, F1, G, H, H1, see the guide to 768/2008 conformity modules. A notified body is involved in every route except module A2, which is only open to capacity serving measures (MI-008, chapter II). The pattern is clear in the table: as soon as an instrument contains electronics or software, the lighter F1, D1 and E1 routes disappear. The choice between B+D, B+F and H1 depends on production volume, quality-system maturity and business model:

B+F: EU-type examination followed by batch verification. Suited to small series or unit production.
B+D: EU-type examination followed by production quality assurance. Suited to stable series, provided a certified QMS is in place.
H1: full quality assurance with design examination. Suited to mature manufacturers certifying several instrument categories.
G: per-unit verification by the Notified Body, reserved for special instruments at very low volume.

Notified Body selection

The Notified Bodies competent for MID are listed in the European Commission NANDO database, with the scope of their designation (MI-00x category and covered modules). See the guide to Notified Body selection via NANDO. A Notified Body designated for MI-001 (water meters) is not automatically competent for MI-003 (electrical meters): the scope of the notification must be verified before any contractual engagement.

The M marking and its format

A MID-compliant instrument carries two complementary markings: the CE marking and the supplementary metrology M marking.

Composition of the M marking

The supplementary metrology marking, defined in Article 21(2) of the directive, is composed of:

The capital letter M and the last two digits of the year of affixing (for example "26" for 2026).
A rectangle surrounding these two elements.

In accordance with Article 22, the CE marking and the supplementary metrology marking are followed, as a separate element, by the four-digit identification number of the Notified Body involved at the production stage (module D, F, H, and so on).

Typical format: CE M26 0123, where "M26" sits inside a rectangle and 0123 designates the Notified Body. The NB number is the one shown in the NANDO database.

Affixing

The CE marking and the M marking must be affixed in a visible, legible and indelible manner on the instrument itself. Where the nature of the instrument prevents this, they are affixed to the accompanying documents and to the packaging, if any (Article 22(1)). For an instrument made of several devices working together, they go on the main device (Article 22(2)).

For the dimensional and visual rules of the associated CE marking, see the guide to CE marking dimensions and visual rules.

Legal meaning

The M marking attests specific conformity to MID requirements, in addition to the CE marking which attests conformity to the applicable directives in the broader sense. A MID instrument bearing only the CE marking without the M marking is non-compliant and cannot be used for legal-metrology purposes, even if the technical documentation is otherwise complete.

MID versus NAWI: the scope split

Directive 2014/31/EU, known as NAWI (Non-Automatic Weighing Instruments), is the twin of MID, published on the same day, aligned on the same 768/2008 architecture, but reserved to non-automatic weighing instruments.

Criterion	MID 2014/32/EU	NAWI 2014/31/EU
Instrument category	Ten categories MI-001 to MI-010 (water, gas, electricity, heat, fuel, automatic weighing, taximeter, material measures, dimensional, exhaust gas)	Non-automatic weighing only
Weighing	Automatic weighing instruments only (MI-006)	Instruments requiring operator intervention during weighing
Typical modules	Per annex, see table above	B+D, B+F, G, and D1 or F1 for some instruments without electronic devices
Marking	CE + M[year] in a rectangle + NB number	CE + M[year] in a rectangle + NB number
OIML recommendation	By category (R 49, R 137, R 46, R 75, etc.)	OIML R 76

A weighing instrument is non-automatic when the operator must intervene during the weighing process (reading, positioning, triggering, validating); it is automatic when the cycle proceeds without human intervention between loading and reading. A shop scale is non-automatic (NAWI). An automatic conveyor-belt weighbridge is automatic (MID MI-006).

The boundary turns on absence of operator intervention, not on the presence of electronics or data transmission. An electronic laboratory balance with a digital display remains non-automatic under NAWI as long as an operator places each sample and validates each reading.

Software for measuring instruments: WELMEC 7.2

WELMEC, European Cooperation in Legal Metrology, is the regional organisation that coordinates the national legal-metrology authorities of the Member States. It publishes application guides that are not legally binding but are widely used by Notified Bodies to assess conformity.

Guide 7.2 on software

WELMEC Guide 7.2, titled "Software Guide (Measuring Instruments Directive 2014/32/EU)", most recently issued as the 2023 version, is the consolidated European reference for software in MID instruments. It describes:

Software classification: software embedded in a purely metrological instrument, software hosting both metrological and non-metrological functions, separate software for downstream processing.
Basic configurations and extensions: type P (built-for-purpose instrument with embedded software) or type U (instrument using a universal computer), plus IT extensions L (long-term storage of measurement data), T (transmission), S (software separation) and D (software download), and instrument-specific extensions I.1, I.2 and so on.
Risk classes: combinations of the required level of protection, examination and conformity to type, from low to high.
Metrology stability requirements: separation between legally relevant and non-relevant functions, integrity of stored data, traceability of updates.
Software-sealing requirements: cryptographic signatures, tamper-evident logs, privileged passwords.
Update requirements: authorisation check, image signature, retention of the update log.

A MID instrument whose software does not follow the WELMEC 7.2 doctrine is rarely certified: European Notified Bodies have adopted this guide as their practical reference.

IEC 60050 vocabulary

The vocabulary applied to software and metrology electronics follows the IEC 60050 standard (International Electrotechnical Vocabulary), notably its chapters 300 (measurement), 301 (electrical instruments), 311 (instruments using an electrical signal) and 351 (control technology). The Notified Body expects documentation using this normative vocabulary to avoid terminological ambiguity.

Articulation with cybersecurity

The scope of WELMEC 7.2 and MID covers metrology stability: that the displayed result remains faithful to the physical measurement. It does not cover general cybersecurity under the Cyber Resilience Act (CRA), whose reporting obligations apply from 11 September 2026 and full requirements from 11 December 2027. The two frameworks are complementary: an MI-003 smart meter will follow WELMEC 7.2 for metrology integrity and the CRA for general cybersecurity.

Verification and market surveillance

Before placing on the market

Under the MID, the conformity assessment module replaces the old national "initial verification": the CE and M markings are affixed before the instrument is placed on the market (Article 22(3)), possibly during manufacture. The notified body involved in production control adds its number.

In service

Subsequent verification in service is outside the MID. Member States that regulate a measuring task set the in-service rules nationally (in France, Decree 2001-387 and its implementing orders), including how often meters are re-verified and the errors allowed in service.

Market surveillance

National authorities (in France the LNE and DGCCRF coordinate; in Germany the PTB; in the United Kingdom, outside the EU, the Office for Product Safety and Standards) carry out market controls: sampling, metrology checks, control of the M marking and the technical file. Non-compliant instruments may be withdrawn from the market, and the manufacturer or importer exposed to sanctions.

For the cross-cutting surveillance framework, see the market surveillance RAPEX guide.

A communicating active-energy electrical meter (smart meter) accumulates several regulatory frameworks:

MID 2014/32/EU annex MI-003: metrology stability, accuracy, accuracy classes, integrity of the energy count.
RED 2014/53/EU: conformity of the radio part (band used, power, spectrum), where the instrument communicates by radio (RF mesh, cellular).
EMC 2014/30/EU and LVD 2014/35/EU: electromagnetic compatibility and electrical safety for parts not covered by MID.
GDPR (Regulation 2016/679): hourly or sub-hourly load curves are personal data from which behaviour can be inferred; processing requires a legal basis and minimisation measures.
Cyber Resilience Act (CRA): vulnerability and incident reporting from 11 September 2026, full requirements for products with digital elements from 11 December 2027.

Multi-directive conformity assessment requires coordination across the functions of each framework. The M marking attests MID conformity; it says nothing about RED, EMC, GDPR or CRA conformity.

Common pitfalls

Generic CE marking without M marking

The most frequent error: presenting a MID instrument with only the classic CE marking, on the assumption that it is enough. A MID instrument without the M marking is not compliant and cannot be used for legal metrology. The presence of the M marking is essential; its absence is a non-conformity immediately detected by market surveillance.

Wrong MI annex

Confusing MI-00x categories leads to applying the wrong MPE grid and the wrong module grid. A heat meter falls under MI-004, not under MI-003 (active-energy electrical). A gas-volume converter falls under MI-002, complementing the gas meter, not under MI-003. The strict reading of Article 2(1) and explicit attachment to an MI annex must appear at the head of the technical file.

Software documentation not following WELMEC 7.2

Submitting a MID file whose software is not documented under WELMEC 7.2 practically always leads to refusal or to a request for additional information. Notified Bodies expect software classification, identification of legally relevant functions, documentation of software sealing and the update log. This documentation must be planned from the design stage, not reconstructed at the end of the project.

Own-use versus commercial-use confusion

A manufacturer assumes in good faith that an instrument sold for "internal energy monitoring" escapes MID. If the instrument is later used to bill a sub-tenant or to declare a regulated consumption in a Member State that regulates that task, it can only be used if it carries the CE and M markings. Better to treat MID as soon as a legally relevant use is foreseeable.

MID confused with NAWI

A shop scale is not covered by MID MI-006 (which covers automatic weighing). It falls under NAWI 2014/31/EU. Conversely, an automatic conveyor-belt weighbridge falls under MID MI-006 and not under NAWI. The boundary turns on the presence or absence of operator intervention during weighing. The confusion leads to applying the wrong evaluation grid and to involving a Notified Body not designated for the actual category.

Forgotten periodic verification

The manufacturer and the importer handle initial verification, but periodic verification in service is often forgotten in the chain of responsibilities. National rules usually place it on the user or owner of the instrument (distributor, network operator, carrier), who must budget for it.

Metrology components substituted without re-evaluation

Under module B, the manufacturer must inform the notified body holding the technical documentation of all modifications to the approved type that may affect conformity; the body decides whether an addition to the EU-type examination certificate is needed. Replacing a sensor or a metrology-relevant electronic module without that step leaves the new version outside the certificate. See the component substitution rules guide.

Claims the text contradicts

Common claim	What the directive says
"Every instrument in the ten categories must be MID-certified"	Article 3: Member States choose which measuring tasks to regulate
"Only harmonised standards give presumption of conformity"	Article 14(2): listed parts of normative documents (OIML) do too
"Module A self-declaration is never possible"	Module A2 is available for capacity serving measures (MI-008, chapter II)
"The same modules apply to all instruments of a category"	MI-006 and MI-009 restrict the routes for electronic instruments and instruments with software
"MID sets in-service errors and re-verification"	In-service rules are national
"WELMEC extension P is protection against modification"	Type P is a built-for-purpose instrument; L, T, S, D are the IT extensions

Articulation with the glossary and the CE pillar

For cross-cutting definitions (Notified Body, EU declaration of conformity, market surveillance, presumption of conformity, NLF, NANDO, etc.), see the glossary and the CE pillar. For the overview of assessment modules, see the 768/2008 modules guide. For the "self-declaration versus Notified Body" criteria grid, see the self-declaration versus Notified Body guide.

Frequently asked questions

What is the difference between MID 2014/32/EU and NAWI 2014/31/EU?: MID (Measuring Instruments Directive) covers ten categories of measuring instruments defined in Article 2(1) and detailed in the instrument-specific Annexes III to XII, numbered MI-001 to MI-010: water meters, gas meters, active-energy electrical meters, heat meters, fuel dispensers, automatic weighing instruments, taximeters, material measures, dimensional measuring instruments, and exhaust-gas analysers. NAWI (Non-Automatic Weighing Instruments) covers only non-automatic weighing instruments, that is, those requiring operator intervention during weighing (shop scales, laboratory balances used for trade). Both directives are parallel, of the same date, aligned on Decision 768/2008/EC.
Which instruments fall under MID and which do not?: Two conditions combine. The instrument must belong to one of the ten categories of Annexes III to XII, and the Member State where it is used must have chosen to regulate that measuring task: Article 3 makes the MID optional, each Member State deciding whether to prescribe the use of regulated instruments for reasons such as consumer protection, fair trading or taxation, and explaining its reasons when it does not. A water meter billed by a distributor in a country that regulates water metering needs MID conformity; the same device used only for internal monitoring does not.
What is Maximum Permissible Error (MPE) and accuracy class?: The Maximum Permissible Error (MPE) is the maximum allowed deviation between the indicated value and the true value, expressed as a percentage or as an absolute value depending on the category. The accuracy class groups instruments by applicable MPE level. The exact values are set by the instrument-specific annex (MI-001 for water meters, MI-002 for gas meters, and so on) and are not transferable from one category to another. The MID sets the errors that apply when the instrument is assessed and placed on the market; errors allowed in service, and the frequency of in-service verification, are set by national rules.
What is the format of the M marking and what does it certify?: A MID-compliant instrument carries two combined markings: the classic CE marking and the supplementary metrology marking, consisting of the capital letter "M" and the last two digits of the year of affixing, surrounded by a rectangle. The rectangle is the same height as the CE marking, and the M marking immediately follows the CE marking (Articles 21 and 22). They are followed by the identification number of the notified body where that body is involved in the production control phase (for example "CE M26 0123"). The absence of the M marking on an instrument that falls under MID is a serious non-conformity: an instrument sold with the CE marking only cannot be used for legal-metrology purposes. The M marking attests specific conformity to MID requirements.
Which conformity assessment modules are allowed under MID?: MID lists, in its Annex II, the authorised modules within the 768/2008/EC framework. The most frequent combinations are B+D (EU-type examination plus production quality assurance), B+F (examination plus product verification), H1 (full quality assurance with design examination) and G (unit verification). Each annex MI-001 to MI-010 lists the modules the manufacturer can choose from. A notified body is involved in almost every route; the one exception is module A2 (internal production control with supervised checks at random intervals), available only for capacity serving measures under MI-008.
What does WELMEC 7.2 say about embedded software in measuring instruments?: WELMEC 7.2 is the consolidated European guide on software in measuring instruments. Published by WELMEC (European Cooperation in Legal Metrology), it describes the requirements applicable to embedded, separate and downloaded software to ensure stability of the metrology functions, data integrity, traceability of updates, and separation between legally relevant and non-legally relevant functions. Notified Bodies rely on WELMEC 7.2 to assess software documentation. A MID instrument whose software does not follow the WELMEC 7.2 doctrine is rarely certified.
What is the link between MID and OIML recommendations?: OIML (International Organisation of Legal Metrology) publishes international recommendations (the "OIML R" series) that serve as the technical foundation for most national legal-metrology regulations, including MID. Each MI-00x category references at least one OIML recommendation: R 49 for water meters, R 137 for gas meters, R 46 for active-energy meters, R 75 for heat meters, R 117 for fuel dispensers, R 51 and R 61 for automatic weighing instruments, R 21 for taximeters. The MID gives OIML documents a role no other New Legislative Framework directive has: under Article 14(2), conformity with parts of normative documents whose list is published in the Official Journal gives presumption of conformity, just like a harmonised standard. OIML certificates themselves do not replace the EU conformity assessment.
Do smart meters fall under MID?: Yes. A communicating active-energy electrical smart meter falls under MID category MI-003 for its metrology functions, and remains subject to other European directives for its non-metrological functions: RED 2014/53/EU for the radio part, EMC 2014/30/EU for electromagnetic compatibility, GDPR for personal consumption data, and the Cyber Resilience Act for product cybersecurity (reporting obligations from 11 September 2026, full requirements from 11 December 2027). MID covers metrology stability and energy-counting integrity; it does not cover data privacy or cybersecurity.