Analyser Precision / Analyser Site Precision. The closeness of agreement between a sequence of analyser results obtained using the same analyser and same sample within a short interval of time under normal site operating conditions. A quantitative measure of the normal expected variability associated with the same analyser in a given location obtaining successive repeat results on identical reference material. It can be defined as that difference between two such single results that would only be exceeded in the long run in one case in twenty. Equivalent to plus or minus two standard deviations or the measurement uncertainty with a 95% confidence level.