What is a verified scale? The green M mark explained

A verified scale is a weighing instrument that has been approved for legal-for-trade use and shows this with a marking on the type plate. This is what that plate tells you.

The green M mark

Next to the CE mark is a capital M in a rectangle, together with the last two digits of the year in which conformity was established and the four-digit number of the notified body that oversees it. Together they say: this instrument complies with directive 2014/31/EU for non-automatic weighing instruments and may be used for the applications the law specifies. Without that mark a scale is an ordinary measuring instrument, however good it is.

The accuracy class

A Roman numeral in an oval: I, II, III or IIII. Class I is the special class of the analytical balance, Class II the fine class of the precision balance, Class III the medium class of retail, bench, floor and pallet scales, and Class IIII the ordinary class for coarse work such as sand and gravel. The class says nothing about quality but about the ratio between capacity and verification scale interval. See OIML classes explained.

Max, Min, e and d

Max is the largest weight the instrument may weigh. Min is the smallest weight for which the weighing is still valid: in Class III, twenty times the verification scale interval. Below that you may not charge by weight. e is the verification scale interval, the step in which the legal tolerance is expressed; d is the readability, the step the display shows. On a Class III scale, e and d are usually the same. On a verified laboratory balance, d is often ten times finer than e: the display shows 0.1 mg, but the law works with 1 mg. The number of verification scale intervals in the range, Max divided by e, determines the class.

The tolerance

A verified instrument may deviate, but not by more than the law allows. In service, for Class III that is one verification scale interval up to 500 e, two up to 2,000 e and three above that. A 15 kg retail scale with e = 5 g may therefore deviate by two steps of 5 grams up to 10 kg. At the initial verification, the permitted deviation is half of that.

The seals

Over the screws of the housing and over access to the adjustment menu there is a seal: a sticker or lead seal that breaks when it is removed. That seal guarantees that nothing in the weighing technology has changed since the inspection. If it is broken, the verification is invalid and the instrument must be re-verified. That is what we arrange with a re-verification; re-verification is arranged through the manufacturer.

When you need one

Selling by weight, calculating tariffs and levies, weighing patients, preparing medicines, analyses in a medical or pharmaceutical laboratory, and determining the weight on a prepackage. All scales that can be supplied verified are listed under verified scales. More about the legal rules under legal-for-trade rules and your scale.

Frequently asked questions

My scale has a CE mark. Does that mean it is verified?

No. The CE mark says that the device is electrically safe and complies with the European product rules. It is only verified with the M in a rectangle next to it.

What does Class III on my scale mean?

The medium class, intended for trade and industry: between 500 and 10,000 verification scale intervals in the range, with a verification scale interval from 0.1 gram. Virtually all retail, bench and floor scales are Class III.

May I weigh below Min?

The instrument will show a reading, but the weighing is not valid there for legal-for-trade use. If you regularly weigh small quantities, choose a scale with a smaller verification scale interval.

How do I know whether a model can be verified?

Only a model with an EU type approval can be verified. In our shop this is shown for every version; for OHAUS and KERN the M is also part of the type designation.