Even if an instrument is calibrated by the manufacturer, environmental conditions, harsh media, shock, or vibration can cause its accuracy to drift over time. This unnoticeable drift can lead to measurement errors, safety issues, expensive repairs, or costly downtime, making periodic calibration essential.

Calibration involves comparing a device's measurement value with that of a known, more accurate calibration reference traceable to a recognized standard. It should be conducted by an ISO-certified lab, ensuring traceability to national metrology institutions like NIST.

During calibration, a device is given known input values across its measurement range. Its output readings are compared to the reference. If a discrepancy exists, adjustments are made to bring the device back into its accepted accuracy range.

After calibration, a lab issues a certificate with a unique ID. This certificate should detail the device, lab, customer, standards used, environmental conditions, procedures, results, technician's signature, and evidence of traceability. Keeping these certificates organized is crucial for auditing and tracking recalibration needs.