Accuracy and Precision

Accuracy

Accuracy is the degree to which the measured value of the quality characteristic agrees with the true value. the difference between the measured value and the true value is known as the error of measurement. A practical difficulty in judging accuracy is that the method employed to determine the true value should be a method of high precision. It is practically difficult to measure exactly the true value and that is why a set of observations is made whose mean is taken to be the true value of the quality measured.

Hence Accuracy is defined as "The closeness of mean value to the true value."

The Mean chart helps to maintain the accuracy of data.

Precision

Precision is the degree which determines how well identically performed measurements agree with each other. Precision carries no meaning for only one measurement. It exists when repeated measurements are made on a single quality characteristic of one particular article, under identical conditions. In such a set, the observations will scatter about the mean. The less this scattering, more precise is the measurement.

Hence Precision is defined as "The closeness of individual values to each other."

The Run chart helps to maintain the precision of the data.