It is the degree of agreement between the measured value and it’s true value. The
difference between the measured value & the true value is known as ‘Error of measurement’.
Accuracy is the quality of conformity.
To distinguish the Precision from Accuracy, the following simple example can be said. A
repaired needle-watch will give Precision readings (same time) all the times, but will give
Accurate readings (correct time) only 2 times in a day.
Of the two, Precision & Accuracy, only the former is required though the latter is usually
sought for in a measuring process. Achieving high precision is easier & cheaper than
achieving high accuracy. If the measuring instrument is of high precise & is calibrated for its
error, then the true value can be easily obtained from the measured average value after
deducting the instrument error. So, high precision - instrument is required rather than the
high accurate – instrument, considering cost and reliability of the measuring instrument.
However, of the two, precision & accuracy, which one is more vital, depends on the situation.
For example, for a carpenter entrusted with the job of fitting a shelf into cupboard, precision
is more important. This can be achieved only when he uses the same scale to measure the
cupboard & the board for shelf. It hardly matters whether his scale is accurate or not. If
however, such a board is ordered for purchase from a pre-cut board from outside, accuracy
becomes more vital than precision. He must measure the size of the cupboard very
accurately before placing the order.
‘Interchangeability’ is the call of the day. Not only a nut from its lot should fit on any bolt of
its lot, both manufactured in the same plant by same men, but also, it should fit on a bolt from
some other manufacturer. The simplest way to maintain compatibility of parts for
interchangeable manufacture is by adopting accuracy in measurement everywhere.