The operation of bringing a measuring instrument into a state of performance suitable for its use, typically by correcting bias, zero offset, or span errors identified during calibration.
Adjustment is the act of modifying an instrument to correct errors found during calibration. This may involve zeroing the instrument, adjusting a potentiometer, applying an offset correction, changing a gain setting, or performing a multi-point linearization. The goal is to bring the instrument's readings as close to the true values as possible across its operating range.
It is important to distinguish between calibration and adjustment. Calibration is the process of comparing an instrument against a reference standard and documenting the results. Adjustment is a separate action that changes the instrument's response. Not every calibration requires an adjustment — if the as-found readings are within tolerance, the instrument is returned to service without modification. Adjustment is only performed when the as-found readings show unacceptable error.
In calibration management, the sequence of recording as-found data before any adjustment and as-left data after adjustment is critical. The as-found data reveals the instrument's condition as it was being used, enabling assessment of the validity of measurements made since the last calibration. The as-left data confirms the instrument's condition as it is returned to service. ISO 17025 and most quality systems require this documentation to maintain traceability and support nonconformance investigations.
In aerospace calibration labs, adjustment is critical for pressure standards used in altimeter testing. When a deadweight tester shows a +0.15% bias during calibration against NIST-traceable standards, technicians adjust the instrument's software coefficients to eliminate this systematic error, ensuring aircraft instruments meet DO-160 accuracy requirements. Medical device manufacturers frequently adjust temperature chambers used for sterilization validation. A chamber reading 2.1°C high at 121°C requires immediate adjustment of its control algorithm before continuing pharmaceutical validation cycles, as this error would invalidate sterility assurance levels per FDA 21 CFR Part 820. Common audit findings occur when labs fail to document adjustment procedures or perform adjustments without proper authorization. ISO/IEC 17025:2017 auditors frequently cite non-conformances when technicians adjust instruments without following written procedures or when adjustment records lack traceability to calibration standards. Another frequent problem: adjusting instruments beyond their design capability, such as forcing a ±0.1% accuracy gauge to meet ±0.05% requirements through excessive adjustment, which masks underlying instrument degradation and leads to unreliable measurements in critical applications.
ISO/IEC 17025:2017 Section 6.4.6 requires laboratories to have procedures for adjustment of equipment, with records maintained for traceability. Section 7.8.6.1 specifically addresses when adjustments are permitted and documentation requirements. AS9100D Section 7.1.5.1 mandates control of measuring equipment adjustments in aerospace applications. ISO 13485:2016 Section 7.6 requires medical device manufacturers to document adjustment procedures and maintain records demonstrating equipment remains suitable for use. ANSI/NCSL Z540.3-2006 Section 9.2.3 details adjustment requirements and the need to verify performance after adjustment. ILAC-P14:01/2013 Policy requires adjustment procedures to be documented and traceable to measurement standards. Auditors specifically examine: documented adjustment procedures, authorization protocols for who can perform adjustments, verification that adjusted equipment meets specifications, and traceability of adjustment standards. ISO 9001:2015 Section 7.1.5.2 requires demonstration that measurement equipment remains capable after adjustment. GUM principles apply when evaluating uncertainty contributions from adjustment procedures.
CalibrationOS handles adjustment through its Equipment Management module, automatically triggering adjustment workflows when calibration results exceed acceptance criteria. The system captures pre- and post-adjustment readings, documents adjustment procedures performed, and records technician authorization levels. Adjustment records include as-found/as-left data, standard uncertainties, and traceability chains to reference standards used for verification. The Certificate Generator automatically includes adjustment notifications on calibration certificates per ISO/IEC 17025 requirements. During audits, the Compliance Dashboard provides auditors with complete adjustment histories, showing procedure adherence and authorized personnel involvement. The system enforces adjustment approval workflows, preventing unauthorized modifications and maintaining measurement assurance. Integration with the Uncertainty Calculator automatically recalculates measurement uncertainties when adjustments are performed, ensuring continued compliance with customer specifications and regulatory requirements.
Calibration is the process of comparing an instrument to a reference standard and documenting the errors. Adjustment is the separate act of modifying the instrument to reduce those errors. Calibration may or may not include adjustment.
An instrument should be adjusted when its as-found readings fall outside the specified tolerance. If readings are within tolerance, no adjustment is needed. As-found data must always be recorded before any adjustment is made.
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