How do you calculate precision?

Accuracy describes the correlation between the measured value and the accepted value. The accuracy of a measurement, or set of measurements, can be expressed in terms of error: The larger the error is, the less accurate is the measurement. Precisiondescribes the reproducibility of a measurement. To evaluate the precision of a set of measurements, start by finding the deviation of each individual measurement in the set from the average of all the measurements in the set: Note that deviation is always positive because the vertical lines in the formula represent absolute value. The average of all the deviations in the set is called the average deviation. The larger the average deviation is, the less precise is the data set.