From time to time over the years I have offered comments about documents purporting to be “as good as” or “the same as” proper calibration reports. Unfortunately, confusion still reigns as one company tries to outdo another. Unless calibration-savvy people review the paperwork, impressive sounding verbiage will continue to send gage buyers down the wrong path. Sadder still, many quality auditors are just as easily led down the same path.
A friend of mine in the industry recently pointed out something I had not adequately covered in previous rants on the subject. The authors of these bits of paper change the document titles to go one better than their competitor, implying their competitor’s document is not the right one, while theirs-with a different title-is the right way to go.
Some of the titles I’m referring to include: Certificate of Compliance, Certificate of Conformance, Certificate of Inspection and Certificate of Accuracy. You’ll note the common word certificate, which means the issuer is certifying something, but that is rarely spelled out in any meaningful way other than to say someone is supposed to have checked something. Rarely is any data presented, but occasionally someone gets clever and throws in some details from a specification. This may be handy information to have, but in the case of gages, the same information is already marked on them.
These documents are usually small pieces of paper with everything on them straight off a printing press. They are supplied free of charge, which is why cost-cutting gage buyers like them. And if their quality auditor accepts them all is well even though they supply little or no useful information.
Getting down to the crunchy stuff, the piece of paper is worth more than what is printed on it.
The gaging industry has traditionally offered what is referred to as either a short form “Cert” or certificate or a long form version of the same thing. The former has limited data, the latter a bit more, but there are no formal rules as to the extent of the calibration performed or reported. But at least there is some helpful information at a very low cost. The American Measuring Tool Manufacturers Association is working to standardize their content so gage users will know exactly what will be calibrated and reported.
ISO 17025 or versions of it is the technical standard many calibration laboratories and some gage manufacturers comply with, but it does not specify report content to any significant extent. This means there are some accredited facilities whose calibration reports are sadly lacking in technical detail when it comes to gages.
The cheapest insurance you can have that a calibration report is worth the paper it’s printed on is if it is issued by a facility accredited to ISO17025 or an equivalent standard. While not perfect, at least you’ll know the outfit issuing it has the hardware and staff capable of doing the job. And this has been verified by an on-site audit by a usually technically competent assessor.
A proper calibration report provides data that will enable you to make decisions respecting the suitability of the gage or instrument for your work. It will also include measurement uncertainty for each parameter calibrated that will be helpful in resolving measuring disputes that may arise. The reported data is essential in determining the next date for calibration.
If the lab in question has been accredited, traceability is confirmed during the on-site assessment when source documents are reviewed for applicability. It doesn’t have to be shown on the calibration report because the lab could not become accredited without it. Having said that, I should note that some other calibration standards require traceability report numbers on calibration reports in addition to a listing of calibration dates for the equipment used. This information is of little value unless the source documents are checked and, in the latter case, an on-site evaluation is done to see if such dates will be effective. Despite this, so many people want some of this information on reports that we list it to avoid wasting time discussing the subject.
One of the downsides of a real calibration report is that it costs money. But it has value because it gives you data-proof that an item was calibrated-compared to a promise and no data from “free” bits of paper that can be issued by anyone.
