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HMRC internal manual

Oils Technical Manual

Measurement: Measurement Instruments Directive (MID)


Known as the MID, details of this and the legislation to bring this EU directive into UK law can be found on the National Weights and Measures Laboratory site at .

The MID sets standards for the operation of most measuring devices sold, putting them into classes of accuracy and laying down the marking and documentation that must accompany any device, so that the user or anyone else checking knows how it should perform and the environment it needs in order to be able to operate properly.

MID and oils assurance

The part of the MID that affects oils assurance directly is in Appendix MI-005 - ‘Measuring Systems for the Continuous and Dynamic Measurement of Quantities of Liquids Other Than Water’. This was put into UK law by Statutory Instrument No 1266; The Measuring Instruments (Liquid Fuel and Lubricants) Regulations 2006 which came into force on 30 May 2006.

The MID specifies accuracy classes, which for simplicity, are named after each class of measuring system’s maximum permissible error (MPE). So, a class 0.3 accuracy has an MPE of 0.3%. The classes are 0.3, 0.5, 1.0, 1.5 and 2.5. The only class that meets our standard is 0.3 - the standard specified in Notice 179.

Please note however that any meter is part of an overall measuring system - for example, a positive displacement meter’s revolutions will be within 0.2% of the volume passed through it, but after an adjustment for temperature affecting density, the reading will be still within 0.3%.

(Please also note, that whilst Notice 179 states that all meters will need to perform within an accuracy MPE of +/- 0.15%, which is what we would expect to see evidenced on any calibration/proving reports for the meter under test, MID has set new standards to replace these current values, for all equipment installed after October 2006).

The MID requires that (a) any measuring system is robust in the conditions within which it is expected to operate ( that is it must be fit for the purposes it is being used for ) and (b) that the conditions under which a meter is designed to operate are easily verifiable.

Not all of the MID is being put into UK Law, for instance Automatic (tank) Level Gauges, (ALGs) are not covered, and whilst measures of length are covered, it is unlikely that this will apply to dipping/ullaging rods and tapes

N.B. We no longer approve meters or ALGs before they are put into service. Instead we now require that all meters or ALGs meet pre-determined levels of accuracy.