Ok so it means that in our procedure we are just checking the scales not calibrating them, right?
I hate to be that guy to split legal hairs (U.S.), but by definitions there is only a legal term of 'calibration' as the comparative values of a measuring device under test to an applied value of a known reference. "Known" being the key definition here of the process. Traceability certs to calibration standards by an authoritative body need to be applied. Normally (U.S.), this is managed by municipal authorities.
You need to have your scales under surveillance of local jurisdictions to satisfy U.S. commerce laws, and in the event of a device used to monitor a critical limit also satisfy USDA, USDC, and USFDA regulations for applied guidance documents.
I've attached a few files for you review provided by NIST which govern this topic:
NIST Handbook 44.pdf 5.29MB
NIST Handbook 133.pdf 3.79MB
Essentially in summary, there is no 'check'. Either a measuring device is verified calibrated to a known reference or it is not.