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Establishment of Calibration Intervals

Updated: Aug 2, 2022

The concept of "calibration interval" is an important one in measurement science. Unfortunately most criminal law lawyers and Judges are not familiar with this concept. It will probably be necessary to lay a foundation respecting this concept during an examination-in-chief or cross-examination of an expert. You may need the help of a metrologist to do so. This is an example cross-examination that needs improvement.


To introduce the concept of "calibration interval" in the international literature.

To introduce the concept of "uncertainty growth" in the international literature.

To begin to connect "reliability" with "calibration interval" and "uncertainty growth" over time.

Q. A paper called Establishment and Adjustment of Calibration Intervals Revising N-C-S-L-I Recommended Practice, R-P-1. Do you have any idea what N-C-S-L-I is? A. No idea whatsoever.

Q. I think N-C-S-L-I.... A. This is the first time I’m seeing this. Q. Oh, is it? Okay. National Conference of Standards Laboratories, and with respect to recommended practice R-P-1. And it appears to be a paper with an author by the name of Mark Custer. The co-author is Doctor Howard Kestra (ph), Miguel Decos (ph) from NASA, Doctor Steve Dwyer, from N-S-W-C Corona and Doctor Dennis Jackson, N-S-W-C Corona. Do you know any of these people? A. I don’t know any of those individuals. This appears to be – this isn’t a peer reviewed article. It appears to be a presentation done at a workshop or a symposium. Q. All right. And.... A. That’s my – that’s what it initially appears to – unless there’s something....

Q. All right. So, just under the word “Introduction” on the first page there’s a suggestion there that “Whether or not it is explicitly recognised and controlled by the calibration laboratory or customer, every calibration is associated with a time period during which the calibration is considered valid and after which it is not.” Now is that consistent with your scientific experience? A. Yes. Q. And just read on, “More precisely the calibrated instrument’s measurement uncertainty increases with time after calibration in a process known as uncertainty growth and its measurement reliability or probably that it will be found in tolerance when calibrated decreases correspondingly.” Is that consistent with your experience? A. It’s a possibility, yes. Q. “And after a certain time period the calibration interval, the increased uncertainty and degraded measurement reliability drives the risk of measurement precision error beyond acceptable levels.” Is that your experience? A. That’s also a possibility, yes. MR. BISS: All right. If that item might be marked as an exhibit please, Your Honour? THE COURT: Exhibit 29 is – it’s looks like an article from 2007 N-C-S-L International Workshop and Symposium. EXHIBIT NUMBER 29: Article from 2007 N-C-S-L International Workshop and Symposium – produced and marked.

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