function of quantities, the value of which, when calculated using known quantity values for the input quantities in a measurement model, is a measured quantity value of the output quantity in the measurement model
NOTE 1 If a measurement modelh(Y, X1, …, Xn) = 0 can explicitly be written as Y = f (X1, …, Xn), where Y is the output quantity in the measurement model, the function f is the measurement function. More generally, f may symbolize an algorithm, yielding for input quantity values x1, …, xn a corresponding unique output quantity value y = f (x1, …, xn).
NOTE 2 A measurement function is also used to calculate the measurement uncertainty associated with the measured quantity value of Y.
ANNOTATION (informative) [2 December 2014] Here "quantity value(s)" can be replaced by "value(s)" without ambiguity: "function of quantities, the value of which, when calculated using known values for the input quantities in a measurement model, is a measured value of the output quantity in the measurement model".