Other Dimensions: Second Opinions
February 1, 2011
I find opinions fascinating because everyone has them, and because many are based on someone else’s opinion, there’s an endless variety of them.
You have to consider the source of opinions when determining their worth. We tend to give more weight to opinions from “experts” in a given field than those of the lay person, but the experts tend to be wrong more than they are right. Opinions from stock market experts are one such example.
The scientific experts of their time once warned us that the world was flat. The newly elected head of the Royal Astronomical Society in England in the mid-1950s was asked about the possibility of space travel. He commented that it was “...utter bilge.” In the 1970s, the experts said we would freeze in the dark due to climate problems.
In dimensional metrology, opinions are often demanded by operators of calibration laboratories because they are considered “experts” in this area. They may be experts in the calibration of equipment but not necessarily on whether the results indicate a pass or fail situation.
I often wonder why they’re asked in the first place, particularly when the operator of the equipment provides the criteria on which the decision will be made. If the operator knows what the requirement is, why doesn’t he just compare the results to it and make the call himself?
Too often the operator doesn’t know what the requirements should be and expects the laboratory to use new gage or instrument specifications as the standard-if they have them. Too often, the new standard the gage or instrument was made to is an unknown. Even if it is known, it should be remembered that they apply to new items, not used ones.
ISO 17025 allows accredited laboratories to issue reports using conformance statements in lieu of data. This is handy for the mathematically challenged but tells the operator little. For example, if the report states that the subject gage “...complies with ASME Standard B1....” no data needs to be supplied but must be available if requested. If you want to know how close the gage is to wearing beyond whatever the acceptable limits are, you’re out of luck. The ISO standard makes it clear that unless otherwise specified, readers of the report will assume that all elements called out in the specification have been verified, which is rarely the case.
What folks are really doing in these situations is downloading the decision making, something their corporate legal counsel would probably advise against. I do find it interesting that some companies trying to reduce costs will accept pass/fail opinions, which often means they’ll be discarding useful instruments or gages before their time.
As I have noted in other columns, the golden rule to acceptability is based on the workpiece tolerance the gage has to check or the instrument has to verify. And it doesn’t matter whether the tool involved is new or used.
Another opinion asked of calibration laboratories is about when the instrument or gage should be next calibrated. Once more, this is the owner of the equipment’s call, not the laboratory’s call. The ISO standard forbids laboratories making such judgment calls but will allow them to put due date on reports or stickers if that information came from the owner of the equipment.
I was not privy to the discussions on this requirement, but I suspect it was designed to cover two potential situations. The first is an attempt to prevent an unscrupulous lab noting overly short cycles to increase business. The other was probably due to the fact that an outside laboratory has no way of knowing all the factors that such a decision should be based on.
It could be argued that the value of opinions is proportionate to how specific they are. The broader their coverage, the greater the inaccuracies or vagueness that can be expected. But there is one group of experts who appear to be breaking that rule. I’m referring to those students of the Mayan calendar that supposedly runs out in December. Some are saying the world as we know it will pretty much end at that time.
That’s pretty specific, but I think I’ll get a second opinion before I pack my jammies and head for the hills.