| Definition: | compact finite object whose acoustic scattering properties are known a priori, by calculation in accordance with a proven model on the basis of knowledge of the geometry, dimensions, and material composition of the target, or a posteriori, by measurement Note 1 to entry: Standard targets whose acoustic scattering properties are known a priori are primary standards. Note that the term "primary standard" used here represents a concept different to that of a "primary measurement standard" as defined in ISO/IEC Guide 99:2007, 5.4. Note 2 to entry: Standard targets whose acoustic scattering properties are known a posteriori are secondary standards, as their measurement depends on devices or methods that themselves require calibration. Note that the term "secondary standard" used here represents a concept different to that of a "secondary measurement standard" as defined in ISO/IEC Guide 99:2007, 5.5. Note 3 to entry: In practice, the maximum standard-target dimension will be small compared to significant spatial variations in the sound signal.
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