Main stamp
The main stamp on a calibratable measuring device identifies the authority ( calibration office , test center ) that carried out the calibration . The year of calibration is also noted.
The main stamps are often in the form of seals (e.g. water meters ) or special labels (e.g. gas pumps , scales ), which must be removed or destroyed before opening or adjusting the measuring device. A measuring device is only considered valid if the main stamp has not been damaged.
The only exception to this is the case that the legal-for-trade device is opened for repair by an officially authorized repairer and after the repair has been carried out, it is provided with a repairer identification (red triangle with repair identification and date). This also only applies if the actual calibration has not yet expired.
Larger and more complex measuring devices have additional security stamps that prevent the measuring device from being opened unnoticed. Security stamps, like the main stamps, are provided with the symbol of the testing authority, but do not have the year designation.
In the European Union, common standards have been set for this, so that calibration marks look very sober in Europe today. In the past, every country had its own calibration system, with some quite imaginative brands.
In Germany, the Physikalisch-Technische Bundesanstalt is responsible for the type approval of calibratable measuring devices; the calibrations are carried out by regional calibration offices in the federal states.