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Alliance Calibration

What is the difference between Calibration and Verification?

Posted by Phil Wiseman on Jan 16, 2017 9:43:40 AM

A quick Google search will show about 500,000 results for verification vs. calibration. Obviously, there is a wide range of answers to what appears to be a simple question.

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Topics: verification, calibration

The word Calibration: What does it really mean?

Posted by Kevin Radzik on Dec 6, 2016 7:01:00 AM


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Topics: Measurement Uncertainty, calibration

Thermometers and Food Safety

Posted by Kevin Radzik on Oct 13, 2016 1:29:47 PM

Keeping Food Safe, with Calibration

I’m a foodie, and I’ve told foodie friends of mine for years that they should never trust their food thermometer unless it’s been calibrated. While doing my weekly shopping the other day I spotted this item. “Smoky Pecan and Bourbon Seasoned Beef Flat Iron Steak.”

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Topics: Standards and Compliance

FAQ's: Measurement Uncertainty

Posted by Kevin Radzik on Oct 10, 2016 7:01:00 AM

FAQ's on Uncertainty

As a certified calibration technician and technical manager for a calibration lab, I’ve fielded a lot of questions from customers on uncertainty over the years. Here are a few of the most common and useful.


  • What is measurement uncertainty?

    Measurement uncertainty is way to quantify the “grey area” that surrounds a measurement. A 1 inch measurement with an uncertainty of ± 0.1 inch means that the “true” value could be as small as 0.9 inch or as large as 1.1 inch, but is most likely very close to 1 inch.


    Does uncertainty need to be on my certificate?

    Yes, a measurement without an uncertainty ends the traceability chain. It is also required by ISO 17025. You may ask to have uncertainty omitted from your certificate, but you should be aware of the consequences.


    Why is my uncertainty more than half the tolerance? What about 4:1?

    It is not uncommon for devices to have a tolerance that is the same as their resolution. When resolution is considered it adds about 0.6 of the resolution to the measurement uncertainty. Test ratios (TAR & TUR) do not consider the unit under test so 4:1 cannot be calculated from the calibration certificate.

You may want to read: TUR: What is it?

    What is coverage factor?

    Coverage factor is how likely the “true” value is to fall within the stated measurement uncertainty. It is typically stated as k=x, where x is some whole number. A k factor of one is approximately 68%, two is about 95% and 3 is 99.7%. Most calibration companies report measurement uncertainty at a coverage factor of k=2.


    Can I just report the uncertainty from the certificate when I calibrate my gages?

    No. The measurement uncertainty from your calibration certificate is just one factor of a proper uncertainty budget which must be created in order to report a proper measurement uncertainty of the device you are calibrating.


    How do I apply temperature uncertainty to my dimensional gages?

    When considering temperature uncertainty in dimensional measurement, you must multiply the coefficient of thermal expansion of the material being measured, by the length being measured, by the temperature uncertainty. When performing the calculation be aware of units and make sure they are the same. For imperial units the units should be (μin/in/°F) *(in)*(°F) and the result will be in μin. When you look up the coefficient of thermal expansion it might be listed with °R (Rankine), these are the same “size” units as °F, just with a different zero.


    What is a scope of accreditation?

    An accredited calibration company will have a published scope of accreditation. This will list the calibration parameters that they have been assessed to perform. In the case of an ISO 17025 accredited calibration company this will also include a CMC (Calibration and Measurement Capability) for each of the parameters listed.


    Why does XYZ company charge extra for uncertainties? Can they do that?

    Because they can, and it is a bit of a “grey area.” If the calibration is not accredited, then there is no requirement. If the calibration is accredited, then the certificate must have “the uncertainty of measurement and/or a statement of compliance with an identified metrological specification or clauses thereof” (ISO/IEC 17025:2005 5.4.1.b). Different accreditation bodies view the second half of this statement differently, and this gave rise to this multitier approach to service offerings. 



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Topics: Measurement Uncertainty

Onsite Calibration: Is it always the best choice?

Posted by Kevin Radzik on Oct 3, 2016 11:48:19 AM

But I Want It Done at My Facility

Onsite calibration services have made the life of the calibration purchaser simpler. No more boxing items up and shipping them off to a lab and then waiting. Yes, waiting while production is down or product is stacking up waiting to be inspected before it can ship. If product isn’t leaving the door, then you’re not getting paid, and that doesn’t make anybody happy.

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Topics: Measurement Uncertainty

Measurement Uncertainty: Dirt Measures

Posted by Kevin Radzik on Sep 19, 2016 6:01:00 AM

Dirt Measures

In our calibration lab we have a saying, dirt measures. This actually means a lot more than just cleaning dimensional gages. It speaks to the fact that sources of measurement uncertainty are everywhere. In metrology speak we call them “contributors” to measurement uncertainty. These contributors are everywhere. We try to minimize their impact on the measurements we perform, but in order to do that we must identify them and then compute their magnitude. For this, blog we will skip the math and focus on identifying sources of measurement uncertainty.

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Topics: Measurement Uncertainty

Measurement Uncertainty: What's that number on my Certificate?

Posted by Kevin Radzik on Sep 6, 2016 9:27:56 AM

What’s that Number on My Certificate?

Measurement Uncertainty, you know it’s there. It’s that plus/minus number on your calibration certificate. You just received your prized possession from your calibration lab and you’ve looked over the whole certificate. All of it except that one number, or maybe you look at that number and wonder why it is different this year from last. Maybe, its larger than it was last year. Does this mean they are less certain about my calibration than they were last year?

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Topics: Measurement Uncertainty

TUR: What is it?

Posted by Kevin Radzik on Aug 29, 2016 11:04:20 AM

TUR: What Is It?


In the world of metrology, the three letter acronyms (TLAs) TAR, TUR, and CMC are routinely bantered about like exam scores. Bigger TARs and TURs with smaller CMCs led to the “Scope Wars” of the 90s and early 2000s.

For the quality professional however, all these TLAs have just made the world of metrology more confusing. The calibration world had just gotten past the NIST numbers argument when people started trying to compare scopes of accreditation with TAR/TUR requirements.

As early as the 1930s the “Gage Maker’s Rule of Ten” was regularly understood to be good measurement practice. The basic concept was that the tool used to make a measurement should be ten times as accurate as that object being measured. This was later codified in the 1960 version of the military standard MIL-C-45662. Oddly enough this statement was removed two years later in the 1962 version MIL-C-45662A.





Test Accuracy Ratio. First officially recommended in MIL-STD-120. Carried through various military specifications until ANSI/NCSL Z540.1

Test Uncertainty Ratio. First codified in MIL-HDBK-1839A and continued in ANSI/NCSL Z540.3

Calibration Measurement Capability. Formerly “BMC” Best measurement Capability.

First codified in ISO Guide 25.

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Topics: Standards and Compliance

FDA 483 Letters: 2nd Quarter 2016 Update

Posted by Phil Wiseman on Aug 9, 2016 3:16:39 PM

You've got Mail!

Well, you really don't want to get this letter from the FDA. The title of the web page says it all:

Inspections, Compliance, Enforcement, and Criminal Investigations.

FDA 483 letters are public records and can be viewed by anyone.

We have reviewed the 2nd quarter 2016 FDA 483 letters issued and see some trends in calibration that you should avoid.

Issuing offices include New York, Baltimore, Kansas City, Dallas, Philadelphia, New jers and, Seattle.

While public records, letters were redacted to remove company names and processes.

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Topics: Standards and Compliance

How Do I Know If My Lab is Capable?

Posted by Phil Wiseman on Jul 28, 2016 3:20:09 PM

Select an ISO 17025 accredited Lab and leave it at that.

This is the approach taken by many consumers of calibration services.

Continue reading to learn why this is not the best approach in selecting calibration services.

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Topics: Standards and Compliance

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Our goal is to provide information regarding calibration and its impact on your quality system.

In addition, we are the Geeks & Freaks of Calibration so we also post about Science for the nerd in all of us.

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If you like our posts please share them. If you have suggestions please let us know. If you have Topic ideas for future posts let us know that also.


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