Precision

Precision is the closeness of agreement between measured quantity values obtained by replicate measurements on the same or similar objects under specified conditions.

Precision is not a quantity and therefore it is not expressed numerically. Rather, it is expressed by measures such as the variance, standard deviation, or coefficient of variation under the specified conditions of measurement

• Conditions of measurement
  Many different factors may contribute to the variability between replicate measurements, including the operator; the equipment used; the calibration of the equipment; the environment; the time elapsed between measurements.
• Variance components
  Variance components are estimates of a part of the total variability accounted for by a specified source of variability.
• Precision profile plot
  A precision profile plot shows precision against the measured quantity value over the measuring interval.
• Variance function
  A variance function describes the relationship between the variance and the measured quantity value.