= Blank indication
A <blank indication> is the measured response obtained when the quantity of interest is assumed absent or not contributing. In <analytical chemistry>, an <analytical blank> supplies the material used for that comparison. The indication is an output of the measurement system; it is neither the material itself nor necessarily a zero reading.<International vocabulary of metrology by JCGM>[VIM3, entry4.2]{ref}
For an invented example, a blank produces5 detector-response units. A sample produces15 units. Under an additive background model, the response attributable to the sample above this blank is10 units. Converting that response into an <analyte> <concentration> requires the appropriate <instrument calibration>. Five detector units do not mean5 micromolar simply because both numbers describe the same measurement sequence.
A <blank value> is obtained when an applicable conversion model expresses the blank response as a measured quantity value.<Compendium of Terminology in Analytical Chemistry by IUPAC>[Chapter1, printed page4, §1.15]{ref} Keeping that conversion explicit prevents confusing an instrument indication with a reported <concentration>. Repeated blank indications also provide information about background variability used in a <limit of detection>. A stable offset and a noisy background can have the same mean while supporting different detection performance; <blank correction> of the mean alone does not make their <standard deviations> equal.
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