Calibration Due Dates: Is Your Auditor Wrong?

As an ISO17025 accredited calibration laboratory we often receive flow down questions from our customers that they receive from auditors.

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I had to read the email several times.  

During our recent CASE Audit (airlines) – the auditor was concerned and gave us an OFI (Opportunity for Improvement) on the following issue: In reviewing certs issued from Alliance, one item was calibrated with a gage that was due to expire in a few weeks.

Calibration Due Dates

Did I understand correctly that using a calibration standard that had been calibrated could be  problem?

Did I understand correctly that  calibrated standards are good until they get close to their calibration due date?


Needless to say there were several emails back and forth on this topic.


It is a reasonable question to ask that when a gage is at the end of its’ calibration cycle – could it be suspect? Should it be trusted?

In this case we are referring to a calibration standard, but the question holds true for all measurement and test equipment.


How can you have confidence in the measurement you are making?


In a previous article What is the difference between Calibration and Verification? we addressed this question. As part of our ISO17025 accreditation requirements we perform intermediate checks. There is a nice explanation in The Difference Between Intermediate Checks per ISO 17025 (AKA “verification”) vs Calibration published by Fluke Calibration.

"Calibration is the process of comparing a device to a measurement standard. Calibration will give you the “error” of your device or sensor, or how far it has drifted from its nominal value, be that a volt, ampere, or a degree of Celsius. The measurement standard itself has been calibrated by a more accurate standard, and this process is repeated until the calibrations are connected. The definition of the measurement unit itself is defined by the International System of units (SI). Fluke Calibration builds measurement standards of several different levels of accuracy to enable people to compare their devices to measurement standards. This is referred to as a calibration “traceable to the SI.” Through a well-defined calibration process in accordance with the international standard, ISO 17025, every device used in a calibration measurement can be traced back to the international standard units. The SI units are maintained by a network of National Metrology Institutes such as NISTBIPM and many others. In summary, when you send a device to a calibration lab, they’ll first calibrate the device to understand how far off of nominal it is, and then do a verification that the device is performing in or out of the tolerance that is defined by the published specifications."

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This article goes on to explain the role of intermediate checks and verification. "Intermediate Checks, or Verifications of Equipment, are measurements of devices in smaller increments of time than your calibration cycle, to verify that it’s still within the bounds of acceptable performance. While it’s typically performed in regulated industries such as pharmaceuticals and medical devices, in other industries it is much less common, especially when there is no regulatory body. Even in some regulated industries, such as aerospace, it’s less common because the FAA only begins its investigation into measurement devices when an aircraft component fails."


ISO17025 does not dictate cycle times.  It requires record keeping and documentation based upon the calibration program we follow.   

Here is an excerpt from Section 6.4 of ISO17025:


6.4 Equipment


6.4.1 The laboratory shall have access to equipment including, but not limited to, measuring instruments, software, measurement standards, reference materials, reference data, reagents, consumables or auxiliary apparatus which is required for the correct performance of laboratory activities and which can influence the result.

NOTE 1 A multitude of names exist for reference materials and certified reference materials, including reference standards, calibration standards, standard reference materials and quality control materials. Reference materials from producers meeting the requirements of ISO 17034 come with a product information sheet/certificate that specifies, amongst other characteristics, homogeneity and stability for specified properties and, for certified reference materials, specified properties with certified values, their associated measurement uncertainty and metrological traceability.

Reference materials should be used from producers that meet ISO 17034.

NOTE 2 ISO Guide 33 provides guidance on the selection and use of reference materials. ISO Guide 80 provides guidance to produce in house quality control materials.

6.4.2 In those cases where the laboratory uses equipment outside its permanent control, it shall ensure that the requirements for equipment of this document are met.

6.4.3 The laboratory shall have a procedure for handling, transport, storage, use and planned maintenance of equipment in order to ensure proper functioning and to prevent contamination or deterioration.

6.4.4 The laboratory shall verify that equipment conforms to specified requirements before being placed or returned into service.

6.4.5 The equipment used for measurement shall be capable of achieving the measurement accuracy or measurement uncertainty required to provide a valid result.

6.4.6 Measuring equipment shall be calibrated when:

— the measurement accuracy or measurement uncertainty affects the validity of the reported results, or

— calibration of the equipment is required to establish the metrological traceability of the reported result.

NOTE Types of equipment having an effect on the validity of the reported results can include:

— those used for the direct measurement of the measurand, e.g. use of a balance to perform a mass measurement;

— those used to make corrections to the measured value, e.g. temperature measurements;

— those used to obtain a measurement result calculated from multiple quantities.

6.4.7 The laboratory shall establish a calibration programme, which shall be reviewed and adjusted as necessary in order to maintain confidence in the status of calibration.

6.4.8 All equipment requiring calibration or which has a defined period of validity shall be labelled, coded or otherwise identified to allow the user of the equipment to readily identify the status of calibration or period of validity.

6.4.9 Equipment that has been subjected to overloading or mishandling, gives questionable results, or has been shown to be defective or outside specified requirements, shall be taken out of service. It shall be isolated to prevent its use or clearly labelled or marked as being out of service until it has been verified to perform correctly. The laboratory shall examine the effect of the defect or deviation from specified requirements and shall initiate the management of nonconforming work procedure (see 7.10).

6.4.10 When intermediate checks are necessary to maintain confidence in the performance of the equipment, these checks shall be carried out according to a procedure.

6.4.11 When calibration and reference material data include reference values or correction factors, the laboratory shall ensure the reference values and correction factors are updated and implemented, as appropriate, to meet specified requirements.

6.4.12 The laboratory shall take practicable measures to prevent unintended adjustments of equipment from invalidating results.

6.4.13 Records shall be retained for equipment which can influence laboratory activities. The records shall include the following, where applicable:

a) the identity of equipment, including software and firmware version;

b) the manufacturer’s name, type identification, and serial number or other unique identification;

c) evidence of verification that equipment conforms with specified requirements;

d) the current location;

e) calibration dates, results of calibrations, adjustments, acceptance criteria, and the due date of the next calibration or the calibration interval;

f) documentation of reference materials, results, acceptance criteria, relevant dates and the period of validity;

g) the maintenance plan and maintenance carried out to date, where relevant to the performance of the equipment;

h) details of any damage, malfunction, modification to, or repair of, the equipment.


As is stated above, an accredited laboratory MUST have a system in place to ensure the validity of its results.

If I had been the auditor, I would have asked:

What procedures does the calibration laboratory have in place to meet the requirements of ISO17025 Section 6.4?


Alliance Calibration is accredited to ISO17025 through ANAB/ANSI. We are audited for conformity to international standards and compliance to our quality management system. Our quality management system specifies our Intermediate Check program. Calibration equipment maintenance and calibration standards intermediate performance checks are conducted on a scheduled basis. We do share our polices and procedures with our customers.  Had the auditor asked, we would have shared our policy and results from intermediate checks.


What happens if a standard does not pass an intermediate check? 


ISO17025 Section 7.10 Nonconforming work is very clear.

Section 7.10.1 The laboratory shall have a procedure that shall be implemented when any aspect of its laboratory or results of this work do not conform to its own procedures or the agreed requirements of the customer...

e) where necessary, the customer is notified and work is recalled;

This means that if a standard failed an intermediate check or if it was found to be out of tolerance upon scheduled calibration the customer would be notified and the proper remedies would be discussed and implemented.


What do you think?

Was the auditor correct?

Please share your thoughts in the comments section.



Phil Wiseman

Phil Wiseman

Phil Wiseman is Chief Marketing Officer at Alliance Calibration. He earned a B.S. in Chemical Physics from Centre College. Phil is an ASQ Certified Quality Auditor and ASQ Certified Manager of Quality/Organizational Excellence.

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