Verification or calibration: what is the difference?
The words are used interchangeably, but they are three different things: verification, calibration and adjustment. Which one you need depends on what you use the scale for.
Verification: the legal inspection
Verification is establishing that a weighing instrument meets the legal requirements, and confirming that with a marking: the green M mark - an M in a rectangle next to the CE mark, with the year and the number of the inspection body. A verified scale may be used where the law requires it: selling by weight, medical weighing, the pharmacy, prepacking and calculating tariffs and levies. The inspection follows European directive 2014/31/EU and standard EN 45501, and after a repair to the weighing technology or a broken seal it must be repeated. What the green M mark means exactly is explained under what is a verified scale.
Calibration: measuring and recording
Calibration is measuring with certified check weights how much the scale deviates from the true value, at several points across the range, and recording that in a certificate with the measurement uncertainty. Nothing is changed on the scale during the calibration itself; afterwards you know how good it is. That is what ISO 9001, HACCP, GMP and BRC require: a demonstrably reliable measuring instrument, traceable to the national standard. Calibration is not a legal requirement and does not replace verification. What such a certificate contains is explained under the calibration certificate explained. If the scale is already showing something different from what you expect, that does not necessarily call for a calibration: why a scale deviates starts with the zero point, the set-up and the environment.
Adjustment: setting it right
Adjustment is setting the scale so that it shows the correct value again, with a reference weight or with the internal adjustment weight that many balances have. After adjustment, the scale is calibrated again to record that it worked. On a verified scale, the adjustment is behind a seal: if you break it, the verification lapses and the instrument must be re-verified.
Which one do you need
| You use the scale for | Required |
|---|---|
| selling by weight, prepacking, tariffs | verified (green M mark), then re-verification after repair |
| weighing patients, pharmacy, medical lab | verified |
| own production, stock, quality control with ISO/HACCP/GMP | calibration certificate, periodically |
| own use without a quality system | check now and then with a check weight |
A verified scale does not automatically come with a calibration certificate, and a calibrated scale cannot simply be used for trade. Many businesses need both: verification for the law, the certificate for the auditor.
What we do
We calibrate with a certificate, at your site or in our workshop, and we handle re-verification: KERN, Adam, OHAUS, Baxtran and Gram have authorised us to repair and recalibrate their instruments, and re-verification is arranged through the manufacturer. We supply new scales verified from the factory - the initial verification is carried out by the manufacturer; see verified scales.
Frequently asked questions
Is a verified scale also calibrated?
No. Verification says that the instrument is within the legal tolerance; a calibration certificate says exactly how much it deviates, with the measurement uncertainty. If you want both, ask for a certificate at the same time as the verification.
May I sell using a calibrated scale?
No. For selling by weight, a verified scale with the green M mark is required, however well it has been calibrated.
What is re-verification?
A new inspection of an instrument that has been verified before: after a repair to the weighing technology, after a broken seal, or - in countries with periodic inspection - when the period has expired.
Can I calibrate the scale myself?
You can check it: put a check weight on the scale and see what it reads. A calibration certificate that an auditor will accept requires certified weights, a fixed procedure and a calculation of the measurement uncertainty.