Accuracy refers to the degree of agreement of the measured dimension
with its true magnitude, while Precision stands for degree to which
an instrument gives repeated measurement of the same standard. In general,
good accuracy not necessarily means good precision, and vice versa. For
example, the following figure illustrates the results of a series of the
measurements for a part. It can be seen that the measuring instrument has
small random error, and thus good precision. On the other hand, the result
also shows that this measuring system has poor accuracy, because there
is a large difference between the true value and the measured values of
the part. This situation also signals the system has a system error.
Figure: Accuracy and Precision of a measuring system
