Other Dimensions: Calibration Reports
I am continuously impressed by the creative genius of mankind when it comes to all types of pursuits. One area that stands out in this regard is that of calibration reports. The greatest works of art and literature are no match for the literary and graphic expressions presented in some of them. Unfortunately, too many of them are designed to foster warm fuzzy feelings of security while saying little or nothing at the same time.
It has been my experience that the more gold foil seals and borders a report has, the more it needs looking into. In short, rather than being impressed by what is there, I wonder what is not there that should be.
As I write this column, I have a free document supplied for a thread plug gage from a prominent tool supplier. It is called a calibration report and some quality auditors will accept it at face value. From my point of view, it’s not worth the lovely paper it is printed on.
It notes that the supplier is an ISO 9001: 2000 registered manufacturer, which is no doubt true, but the issuer of the report does not make thread gages so that carries no weight with me. Similarly, both go and no-go pitch diameter values are shown, and in one of the most striking coincidences of my career, both are the exact nominal values that would be marked on the handle. While I am comforted in knowing the gage has been inspected by highly trained personnel, I lose that feeling when I note that the report is undated, unsigned and has no uncertainty statement. The gage is not uniquely identified, the report is not numbered and no calibration procedure is referenced. Because this document is supplied free of charge, my guess is that a clerk in the office filled it out.
A document from an actual gage maker, called a certificate of accuracy, says the gages referred to have been inspected with equipment that has been calibrated and is traceable to NIST. It then declares that it is not a certificate of calibration. It also states that the gages in question have been inspected to four decimal places only. It makes me think someone grabbed a micrometer and did a spot check on them.
Another report from someone who sells rather than makes-or calibrates-gages notes that the gages have been inspected by “trained metrology personnel...using procedures and equipment in accordance with...” a number of well-known standards are then listed. The only problem with this is that the standards listed do not specify procedures and equipment to be used for calibration.
There is a flip side to these shortcomings that is just as questionable. By this I mean reports decorated with extensive quotations from standards for every element that is supposed to have been calibrated. I’m left wondering when four sentences describing the element in question is followed by the notation “OK” as the measured result.
Some quality standards still allow reports from the original equipment maker even though many of them do not have calibration facilities that are correctly accredited. Knowing this, many makers avoid having their capabilities assessed by someone who knows calibration. It also means they can continue issuing “reports” when only a few gages in a batch have actually been calibrated.
Despite the foregoing, there are laboratories that issue reports that are accurate with correct detail, and most important, an uncertainty statement that makes sense. Invariably, they have been correctly accredited to ISO 17025 and/or ANSI/NCSL Z540 standards by a reputable agency that is recognized nationally and internationally. Yes, their calibration costs more, but then what’s a suspect report at half the price or free really worth when it doesn’t meet any recognizable standard?
If you want to know what a meaningful calibration report should have in the way of detail, get a copy of ISO 17025 or ANSI/NCSL Z-540 standards-everything is clearly listed. You can’t beat having a copy of the standards that apply to this field. It’s an easy way to ensure you get what you think you are getting when it comes to calibration.
The reports referred to in this article will be filed in my extensive collection. I refer to it for a laugh when I’m having a bad hair day. However, due to the nature of their contents, they have to be kept in a sealed plastic bag so the odor they emit doesn’t spread around the office.