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Dilip Shah is the president of E=mc3 Solutions and he sat down with Michelle Bangert at the MAX Show in Nashville to talk about his presentation there and more.

Michelle: So, at the session, you're going to talk about calibration reports. Can you tell us a little bit about what your session will discuss?

Dilip: Yes. So, my session is going to talk about how do you assess a calibration report where you calibrate something to a nominal value and you compare it to a specification or tolerance. And traditionally, if the measurements within the tolerances, that's considered a pass. If it's beyond the tolerance limits, it's a fail.

But now you have a thing called measurement uncertainty associated with making that measure. When you take that into consideration, now you have four possible scenarios. Pass, fail, conditional pass, conditional fail.

And so, what it says is that there may be a certain risk associated with making any one of those four statements of conformity. Then there are different decision rules associated with making that conformity statement. And different decision rules have a different risk built into those decision rules.

So, it gets a little bit more complicated than that. For example, let's use a tire pressure gage. The tire pressure gage could be used to check your bicycle's tire pressure. When you use it for that, and let's say it's not right, and you under-inflate your bicycle tire or over-inflate your bicycle tire, that risk, the worst you could do is you could have a flat tire.

You may fall off your bike, but you could get out of it. So, there's a very minimum risk. The same tire pressure gage to check your automobile tire pressure, that may have a little bit more risk associated.

Now imagine using the same pressure gage, checking the tire pressure of a passenger aircraft jet. And you could see the same gage, different risk, making that statement of conformity.

So, one decision rule may apply to checking the bicycle tire pressure and a different tighter decision rule may apply to a passenger jet. And that's what calibration involves. What has happened is technology is evolving so fast that the standards used to calibrate that tire pressure gage, they can't keep up with the better tire gages you have.

Now, I have a story. Several years ago, I bought four cheap tire pressure gages from Walmart. They're five bucks a piece. And then the metrologist got into me. So, when I brought it home and I said, I wonder if they all read the same. Now, I didn't have a standard at home, but I had inflated tires. I said, if I check them, they should all read the same.

Guess what? Between the four, there was a difference of 7.5 PSI. That's a lot. So, I said, obviously, I'm not going to use these gages. But since I train in metrology, I said, I'm going to keep this. It'll be like training aids to show the same concept to students. And then I ended up buying a Michelin digital tire gage with a resolution of 0.1 PSI and then checked them against my standard inflated tire. And they were within 0.1 PSI.

So, you could see the risk with that Walmart pressure gage versus this $15 pressure gage that I got from Amazon. And so, that's a great way to, like I said, differentiate between. You could have the same instrument with different accuracies. different uncertainties, different resolution, and all of those contributors went into the measurement uncertainty.