A test report is only as trustworthy as the instruments that produced it. Calibration — the documented comparison of a measuring instrument against a reference standard — is what links everyday laboratory measurements to national and international measurement standards.
Testing laboratories operate scheduled calibration programmes: each instrument has a defined calibration interval, and results are recorded so that measurement traceability can be demonstrated at any time. If an instrument drifts outside its tolerance, previously issued results are evaluated for impact.
This discipline is invisible to most clients, but it is a core reason why certificates issued on the basis of accredited laboratory testing are recognized and trusted by authorities and by the market.