Legal verification or calibration - when must a scale be verified?

Legal verification or calibration - what is the difference?

Legal verification is an official, legally mandated act: a verified scale may be used in commercial transactions because its readings are deemed legally correct. Calibration, by contrast, is voluntary and merely documents how far a reading deviates from the true value - with no legal force of its own.

A scale is subject to verification whenever the weighing result forms a basis for money, law or health. This includes selling by weight, pharmacies, the production of prepackaged goods and official or medical applications. Operating such a scale unverified risks a fine under the applicable measurement and verification law.

• Selling by weight (butcher, market, delicatessen) - verification required.
• Pharmacy and medicine preparation - verification required.
• Production of prepackaged goods - verification required.
• Medical use, e.g. medical personal scales - verification required.
• Internal control, recipes or R&D without trade - calibration usually suffices.

What accuracy classes exist and what do they mean?

Non-automatic weighing instruments are divided into four accuracy classes, marked with the Roman numerals I to IIII. The decisive figures are the verification scale interval e and the number of intervals n. The finer the resolution, the higher the class.

The verification interval e is the smallest unit for which the error limits apply - it must not be confused with the display step d. In class III, e is often 1 g to 5 g while the display d may be finer. In service the maximum permissible error in use is twice the error limit at verification.

How does MID conformity assessment work?

Since 2016 new non-automatic scales no longer undergo classic initial verification. Instead they undergo conformity assessment under EU Directive 2014/31/EU (the NAWI directive within the MID framework). The manufacturer places the scale on the market in conformity, after which re-verification by the authority begins.

• CE marking plus a green M on a black background (metrology marking).
• Four-digit number of the notified body directly next to the M.
• Accuracy class I, II, III or IIII shown inside an oval.
• Max, Min, e and d stated on the data plate.
• Declaration of conformity from the manufacturer, which you should keep.

Which periods and duties apply in operation?

Legal metrology rules require a verified scale to be re-verified regularly. For non-automatic scales the re-verification period is usually 2 years. The period ends on 31 December of the expiry year, leaving a small buffer before the repeat is due.

The operator, not the manufacturer, is responsible for timely re-verification. In addition, the use of a new or renewed scale must be notified to the competent verification authority within six weeks. Once the verification validity has expired, the scale may no longer be used in commercial transactions.

Frequently asked questions