Test & Inspection
Other Dimensions

Auditors Guide to Calibration Reports

A document without data is not much of a report

I regularly take shots at quality auditors for some of their antics but thought that, in the interest of fairness, it was time to turn my sights on issuers of calibration reports for some of their antics. Auditors are often subjected to blizzards of snow from some of them such that they can find it difficult to dig their way out. In fact, many users of outside calibration services find themselves in a similar situation so I hope the following notes will help them as well.

The first order of business is to define what we’re talking about. Simply put, the document we’re dealing with is a report of values determined by the calibration of a gage or instrument. It is my opinion that a document without data is not much of a report and is essentially useless for using or managing the equipment used for controlling product quality.

This means that documents with simple ‘pass/fail’ notations or certificates of compliance are of little or no benefit and do not constitute a real calibration report.

Many standards such as ISO 17025 and aerospace or nuclear industry versions of them are usually pretty clear on what the report should contain but here, in no particular order, are some examples:

The name and address of the laboratory that actually did the work. A statement that the work was done by a lab that is ‘compliant’ with a related standard is an example of someone skating around in circles.

The laboratory should be accredited by a reputable agency. That accreditation should be clearly stated so you can go to the agency’s web site to confirm it if a copy of the certificate and scope of accreditation is not on hand when it should be.

Measurement uncertainty applicable to each reported measurement should be stated in the same manner as the measurement. For example, if an inch measurement is reported, the associated uncertainty should be expressed in similar terms.

The laboratory’s scope should show that it is accredited for the measurements on the report. There will be occasions where some of the work may not be accredited, in which case the report should clearly note this.

The uncertainties shown on a scope may be different from those on the report you receive. This is usually the case for work done at the customer’s facility rather than the controlled environment of the laboratory. You may have identical items calibrated at the same time in the same laboratory and have different uncertainty values for each on the report due to the physical condition of the items being calibrated.

The laboratory may reference a relevant specification for a particular measurement which outlines what needs to be calibrated. This can leave the recipient with a warm fuzzy feeling that is short lived when it is discovered the item was not calibrated in complete accordance with the specification. Such deviations should be noted on the report so there is no misinterpretation of the results.

Laboratories accredited to ISO 17025 do not need to show traceability to the national standard as it is verified on site by the assessors from the accrediting agency. However, many people assume it has to be specified so all sorts of references to NIST, for example, may be included. But if you don’t know how many levels down the food chain the lab is relative to the actual item calibrated by NIST, the references aren’t worth much.

Calibration reports are meant to be just that: a report of dimensions or performance of the items in question. What is acceptable is best determined by the user’s needs, not interpretations by someone not familiar with them. Some facilities note new product specifications for guidance purposes but the final decision on acceptability is left up to the user as it should be.

Re-calibration dates on reports are not a requirement of ISO 17025 which notes that if the user wants them on the reports, the user, not the laboratory must determine the intervals. That fact should be noted on the report, otherwise the reader of it might assume the laboratory endorses them.

 There are several similar specifications that are copies of ISO 17025 with a few add-ons that could cause a lot of problems. As always, have the source document on hand so you don’t miss them. 

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