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DUI Metrology Dictionary


VIM 2.39 operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication.

To conduct a calibration you need:

First step
- measurement standards (note this is plural)
- corresponding indications (note "with associated measurement uncertainties")
- establish quantity values with measurement uncertainties
Second step
- use this information to establish a relation
- for obtaining a measurement result
- from an indication (which is not the same thing as a measurement result)

The relation needs to be established, however, at all points on the indication axis. Instrument response, particularly on an IR instrument, will not be the same ratio to measurement result at all points (e.g. 20 mg/100Mls to 400 mg/100Mls).

A calibration requires multiple external standards because one cannot assume linearity. Have a look at a university textbook such as Skoog and West, "Fundamentals Of Analytical Chemistry", the one pictured below to understand how a calibration creates a "calibration curve".

A "calibration" is not the same thing as a "control test".

A "system calibration check" English section 320.31(1) or French section 320.31(1) "un test d’étalonnage" therefore connotes calibration checking of one or more complete systems across their measuring interval. An Intoxilyzer 8000C has many systems that need to be in proper working order to achieve reliable results. Each of those systems, including the one that connects instrument electronic response to alcohol in the sample chamber to indication of BAC on the display, needs to have good linearity, throughout the system's measuring interval (eg. 20 to 400 mg/100mLs). A single point control test (e.g. at 100 mg/100MLs) does not adequately check linearity of the BAC measuring system; it does not adequately check calibration across the measuring interval.

"Measuring interval" and "calibration interval" are very different concepts! See their separate definitions in

Skoog and West, Fundamentals Of Analytical Chemistry cover
Link to blog articles on calibration of an approved instrument
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