accuracy

of: a measurement or value

is: a measure of the extent to which the measurement (or value) differs from the true value. [P1.1]

is also: a measure of the extent to which the measurement (or value) is free of systematic error. [P1.1]

linguistically is: perverse. The greater the accuracy, the smaller is its numerical value. A clearer way of expressing it is to say that a quantity is 'accurate to within plus-or-minus so-much'. [P1.1]

Compare with precision.