What calibration establishes
Calibration compares indication against a reference across defined points and conditions. The result can show error, correction and uncertainty information. Whether the instrument is acceptable depends on the applicable tolerance or decision rule.
Adjustment is a separate action
If calibration reveals unacceptable performance, the instrument may be adjusted. After adjustment it is commonly checked again so the final condition is documented. Keeping calibration and adjustment conceptually separate preserves useful history.
As-found and as-left
As-found results describe the instrument before adjustment. As-left results describe it after any permitted adjustment or repair. Losing as-found data can hide drift that may have affected past process decisions.
Metrological traceability
Traceability connects a measurement result through a documented, unbroken chain of calibrations to stated references, with each link contributing uncertainty. A certificate number alone does not explain the quality of that chain.
Calibration interval
Intervals should reflect risk, stability history, manufacturer information, usage, environmental severity and applicable quality requirements. Shorter is not automatically better; the objective is adequate confidence at appropriate cost.