Every lab balance drifts with temperature, wear and time. Calibration is the discipline that keeps its readings meaningful — and for regulated labs, documented.
Internal calibration means the balance carries a motorised reference weight and can recalibrate itself at the press of a button (or automatically when it senses temperature change). It's the right choice for busy QC labs because it removes operator variables.
External calibration uses certified reference weights placed by the operator. It's cheaper to buy and perfectly valid — provided the weights themselves are certified and handled properly (tweezers, never fingers).
Traceability is what auditors look for: an unbroken chain of comparisons linking your balance's calibration to national measurement standards, evidenced by certificates. A calibration performed with uncertified weights may make the balance accurate, but it isn't traceable.
Set a calibration schedule based on use: internal calibration daily or per-session, professional traceable calibration annually at minimum. Log every calibration — the log is as important as the act.