Calibration
Comparison of an instrument's readings with an appropriate reference under specified conditions.
Example
A gas-flow meter may require periodic checks against a traceable standard.
The catch
Calibration does not guarantee correct installation or uninterrupted performance.
In more depth
Calibration, explained.
Calibration tells you how far an instrument's readings sit from the truth, and with what uncertainty, before you rely on them. Adjusting the instrument is a separate step, and the certificate should record the error found before any adjustment as well as after. The before-and-after record is what lets you judge past data, because a meter that fails its check casts doubt on every reading since the last good one.
Methane projects lean heavily on a flow meter and a gas analyser, since the methane destroyed is calculated from gas flow rate and methane concentration. Monitoring rules often require calibration at set intervals and conservative treatment of data when a check is overdue. The calibration dates and the traceability of the reference belong in any monitoring report.