As-Found and As-Left Calibration: Backwards Traceability and Forward-Looking Quality Control
Assessment of Performance Before and After Service for Reliable Balance and Scale Results
When you rely on balances and scales, you need to know reliably how they perform both before and after any service interventions. “As-found” and “as-left” calibration data serve two distinct goals:
As-found data shows how accurately your device performed prior to any adjustment.
As-left data demonstrates the performance after adjustment and defines the accuracy you can expect going forward.
Documenting both sets of data not only helps you decide if your balance or scale meets your needs but also fulfills the requirements of most common standards, such as ISO9001:2015, ISO/IEC 17025, GMP, and various pharmacopoeias.
We offer a globally harmonized approach to as-found and as-left weighing instrument calibration to satisfy all your calibration needs. Get all your results and answers in one document.
What Is As-Found Calibration?
As-found calibration captures the condition of your balance or scale before the service technician makes any corrections. As-found calibration helps to identify any issues that may have arisen since the last calibration, so you can proactively get ahead of negative consequences, identify the root cause and try to avoid potential issues in the future.
As-found calibration results tell you:
Drift or wear that has occurred since the last calibration
Whether your instrument was within tolerance prior to adjustment
By analyzing as-found data your weighing processes become more transparent, while enabling you to track long-term performance trends and ensure long-term compliance with industry standards.
This is also sometimes referred to as “as received”.
= the past
= as-found calibration data
= date of calibration
What Is As-Left Calibration?
As-left calibration quantifies the performance after corrective actions, which include adjustment. It is necessary to perform an as-left calibration if actions were taken on the instrument after the as-found calibration, which alter its performance. Such actions could be:
Adjustment
Internal cleaning
Turning the instrument on its side
Change of instruments’ settings
Manipulation with tools on the instrument
As-left calibration results confirm the accuracy you can expect from the instrument in routine operation after all service activities. Of course, it should also document that the instrument is fit for purpose.
An as-left certificate provides proof of the weighing accuracy of the instrument after the technician’s visit.
This is also sometimes referred to as “as returned”.
= date of calibration
= as-left calibration data
= the future
Benefits of Having As-Found and As-Left Data
- Quality Assurance: Compare before-and-after results to quantify weighing performance over time.
- Regulatory Compliance: Mandatory for ISO/IEC 17025, GMP, FDA, and many pharmacopoeias.
- Decision Basis: Determine if your balance or scale remains fit for purpose in terms of accuracy.
- Audit-Ready Records: Get peace of mind while maintaining full traceability for internal and external audits.
= the past
= as-found calibration data
= date of calibration
= as-left calibration data
= the future
Our Calibration Process – By a Qualified METTLER TOLEDO Service Technician
Calibration as-found:
Records as-found measurements with certified test weights under controlled conditions.
Assessment of performance:
Checks if the instrument’s performance meets your needs. If this is not the case, an adjustment or other activities may be required.
Adjustment (if required):
Improves the instrument’s performance based on calibration results. METTLER TOLEDO balances and scales can only be adjusted by METTLER TOLEDO qualified service technicians with our proprietary software.
Calibration as-left (if required):
If the instrument’s performance is changed after as-found calibration, an as-left calibration is necessary. Actions that necessitate an as-left calibration include adjustments, manipulation with tools, and changes to the instrument’s settings.
Assessment of performance:
Checks if the instrument’s performance meets your needs.
Certificate delivery:
As-found and as-left results delivered in one comprehensive report. This provides peace of mind and audit readiness with documented proof of satisfactory performance.
Benefits of Balance and Scale Calibration
Consistent Quality
Achieve consistent product quality through reproducible results.
Reduced Costs
Reduce material waste and the cost of rework.
Full Compliance
Be audit-proof at all times with appropriate quality management processes.
Frequently Asked Questions (FAQ)
Why is an as-left calibration not enough?
As-found and as-left calibration is required for everyone that wants to fulfill standards and regulations and have peace of mind in audits.
When you only assess performance after maintenance and adjustment have already happened (as-left calibration), you do not have a clear traceability and evidence of conformity of your prior measurements (as-found calibration). This can raise quality concerns. Hence, as-found and as-left calibration is specifically required by more and more standards and regulations, such as ISO9001:2015, ISO/IEC 17025, GMP, and various pharmacopoeias.
What should I do if my as-found calibration failed?
If there is an issue with as-found calibration, question all weighing results since the last accepted calibration and assess their impact. An organization's quality management systems may provide guidance on further actions, so you can proactively get ahead of negative consequences, identify the root cause and try to avoid potential issues in the future. Depending on the severity and or potential risks the appropriate corrective and preventive actions should be taken to ensure you do not compromise your product or measurement quality.
In case of an as-found calibration failure, our service teams are best placed to make the corrections needed to improve performance before as-left calibration. Only METTLER TOLEDO Service technicians can perform the proprietary adjustment that optimizes the performance of METTLER TOLEDO instruments. Further, we have the expertise to guide you on establishing a routine testing plan to help minimize the risk of performance issues between calibrations and help to avoid AF failure to happen in the future.
How often should I perform as-found and as-left calibration?
Typically, every 6 to 12 months, depending on usage, criticality, and environmental factors.
To find out the right frequency based on your situation and risks, the GWP Verification offers a quality assurance plan for balances and scales, containing:
Calibration and service frequency
Routine testing plan, including the frequency, methods, weights and tolerances
Together, these documents create a concrete and audit-proof quality assurance plan for the routine operation of your weighing devices.
What’s the difference between calibration and adjustment?
While calibration states how a weighing device behaves (through quantifying measurement uncertainty under operating conditions onsite), adjustment changes its behavior. When a service technician adjusts a device, they modify its indication in a way that allows the indication to correspond—as much as possible—to the reference weights applied.
