NOTE 2 The term “measurement accuracy” should not be used for measurement trueness and the term “measurement precision” should not be used for 'measurement accuracy', which, however, is related to both these concepts.
NOTE 3 'Measurement accuracy' is sometimes understood as closeness of agreement between measured quantity values that are being attributed to the measurand.
ANNOTATION (informative) [5 June 2014] Here "quantity value" can be replaced with "value" without ambiguity: "closeness of agreement between a measured value and a true value of a measurand".
ANNOTATION (informative) [9 June 2016] Historically, the term "measurement accuracy" has been used in related but slightly different ways. Sometimes a single measured value is considered to be accurate (as in the VIM3 definition), when the measurement error is assumed to be small. In other cases, a set of measured values is considered to be accurate when both the measurement trueness and the measurement precision are assumed to be good. Sometimes a measuring instrument or measuring system is considered to be accurate, in the sense that it provides accurate indications. Care must therefore be taken in explaining in which sense the term "measurement accuracy" is being used. In no case is there an established methodology for assigning a numerical value to measurement accuracy.