Every legally verified scale carries a type plate or sticker with a series of marks and figures. For those who work with it every day, it often looks like a code. Yet it states exactly what you need to know: whether the scale is verified, which accuracy class it falls into and for which range the verification applies.
In this article we go through the type plate step by step, explain what the seals mean and discuss a worked example. If markings are missing or a seal is damaged, re-verification is required; see scale verification and re-verification.
The metrology marking: CE and M
A verified scale carries two markings side by side:
- the CE marking, which indicates that the product complies with the European rules that apply to it;
- the supplementary metrology marking: a capital M with the last two digits of the year, together in a rectangle, followed by the identification number of the notified body.
The year indicates when the marking was affixed. The number refers to the notified body involved in the conformity assessment. Together they show that the instrument was assessed when placed on the market in accordance with European Directive 2014/31/EU on non-automatic weighing instruments.
Note: the CE mark alone says nothing about legal verification. Many scales carry a CE marking and are still not verified. Only with the M marking is the instrument suitable for legally regulated applications, such as selling by weight. The difference from calibration is explained in calibrating, adjusting and verifying scales.
The accuracy class: I to IIII
The class appears as a Roman numeral in an oval on the plate. The classification corresponds to OIML R76 and EN 45501:
| Class | Name | Typical application |
|---|---|---|
| I | special | analytical balances in laboratories |
| II | high | precision balances |
| III | medium | retail, bench, floor and pallet scales, many weighbridges |
| IIII | ordinary | coarse applications |
The class is not a quality score. It is linked to the ratio between the range and the verification scale interval and determines which tolerances apply. A class III scale is therefore not a poor scale, but an instrument made for a different purpose than an analytical balance.
The class also determines which check weights are suitable. As a rule of thumb, the error of the check weight should be no more than one third of the permissible error of the scale at that load. For many class III scales, this leads you to M1 weights. Read more in which calibration weight do I need.
Max, Min, e and d
Alongside the class, the plate shows four items that describe the range and the resolution of the verification:
- Max: the maximum capacity. Above Max, a weighing is not valid.
- Min: the minimum capacity. Below Min, the scale does show a value, but the relative error is too large for a valid legal weighing.
- e: the verification scale interval. This is the step in which the statutory tolerances are expressed.
- d: the readability, the smallest step the display shows. On class III scales, d is usually equal to e. On some balances in classes I and II, d is smaller than e, for example d = 0.1 mg with e = 1 mg.
The number of verification scale intervals n is Max divided by e. That figure partly determines which class an instrument falls into. If a scale has several weighing ranges, Max, Min and e are stated for each range.
A type plate as an example
Suppose you find the following on a bench scale in a butcher's shop:
- the CE mark, with M26 in a rectangle and a four-digit number next to it;
- the Roman numeral III in an oval;
- Max 15 kg, Min 100 g, e = 5 g, d = 5 g;
- make, type and serial number.
This means the following:
- The metrology marking was affixed in 2026, and the number belongs to the notified body involved in the assessment.
- It is a class III scale, intended for trade among other things.
- You may weigh up to 15 kg with it. Below 100 g, a weighing is not valid for charging a customer.
- The tolerances are expressed in steps of 5 g, and the display also shows steps of 5 g.
- The number of verification scale intervals is 15,000 g divided by 5 g, so 3,000.
If any of this information is missing or the plate is illegible, that is a point of attention during an inspection or verification. In practice we mainly see faded stickers on scales that are frequently cleaned with aggressive agents.
Seals: what they protect
Seals are stickers, lead seals or other closures over the access to the adjustment and the weighing mechanism. They are made so that they break or are visibly damaged if someone removes them. On electronic scales, access to settings is sometimes also protected in the software, for example with a counter that records how often metrological settings have been changed.
If a seal is broken, the verification is no longer valid, even if nothing about the scale has been changed. The scale may then no longer be used for legally regulated applications until it has been verified again. How to go about that is explained in re-verification after repair.
Some tips from practice:
- Check the seals at every interim check and record this.
- Do not paint over or tape over seals, and clean them carefully.
- Have a scale with a loose or damaged seal assessed immediately.
- After a verification, take a photo of the type plate and the seals. This helps with later questions.
How MASSLAB helps you
MASSLAB is a Recognised Verifier (Erkend Keurder) under the Dutch Metrology Act and re-verifies verified scales after adjustment, repair or a broken seal, once we have checked that we are permitted to verify that specific instrument. For your quality system we calibrate scales of all makes according to EURAMET cg-18, on site or in our laboratory; see scale calibration. If you are unsure what your type plate says, send us a photo via contact.