[VIM3] 2.52 influence quantity

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quantity that, in a direct measurement, does not affect the quantity that is actually measured, but affects the relation between the indication and the measurement result


EXAMPLE 1 Frequency in the direct measurement with an ammeter of the constant amplitude of an alternating current.

EXAMPLE 2 Amount-of-substance concentration of bilirubin in a direct measurement of haemoglobin amount-of-substance concentration in human blood plasma.

EXAMPLE 3 Temperature of a micrometer used for measuring the length of a rod, but not the temperature of the rod itself which can enter into the definition of the measurand.

EXAMPLE 4 Background pressure in the ion source of a mass spectrometer during a measurement of amount-of-substance fraction.

NOTE 1 An indirect measurement involves a combination of direct measurements, each of which may be affected by influence quantities.

NOTE 2 In the GUM, the concept 'influence quantity' is defined as in the second edition of the VIM, covering not only the quantities affecting the measuring system, as in the definition above, but also those quantities that affect the quantities actually measured. Also, in the GUM this concept is not restricted to direct measurements.



2 Measurement