Title: Shewhart means chart
Long Title: IUPAC Gold Book - Shewhart means chart
DOI: 10.1351/goldbook.08127
Status: current

Definition
Shewhart control chart in which the means of measured quantity values are plotted against time.
Figure 1: Shewhart means chart of the means of duplicate analyses of a quality control material, twice per day (d) over 20 days. Each point is the mean of the day’s four results (\(n = 4\)). Upper and lower warning limits (UWL and LWL) are at \(\bar{x} \pm 2s/\sqrt{n}\), where \(\bar{x}\) is the process mean, \(s\) is the standard deviation under repeatability conditions of measurement, and upper and lower action limits (UAL and LAL) are at \(\bar{x} \pm 3s/\sqrt{n}\). A simulated measurement bias of one standard deviation is applied after day 10.

Note
Nordtest terms a control chart with measured quantity values scaled by the mean or target value an "X-chart". ISO uses the term "X-control chart" for a control chart which plots single values.

Example
A Shewhart means chart with mean values from a process in a state of statistical control with a simulated change in the process mean after 10 days is shown in Fig. 1.

Related Terms
- Shewhart control chart: https://goldbook.iupac.org//terms/view/08125
- quality control material: https://goldbook.iupac.org//terms/view/08107
- repeatability conditions of measurement: https://goldbook.iupac.org//terms/view/08040

Source
- PAC, 2021, 93, 997. 'Metrological and quality concepts in analytical chemistry (IUPAC Recommendations 2021)' on page 1040 (https://doi.org/10.1515/pac-2019-0819)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/08127/html
- json: https://goldbook.iupac.org/terms/view/08127/json
- xml: https://goldbook.iupac.org/terms/view/08127/xml

Citation: Citation: 'Shewhart means chart' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.08127
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Accessed: 2026-05-30T10:29:29+00:00