{"term":{"id":"08069","title":"control limit","longtitle":"IUPAC Gold Book - control limit","doi":"10.1351\/goldbook.08069","code":"08069","status":"current","definitions":[{"id":1,"text":"Value defining an intended level of stability for a process.","notes":{"1":"A control limit may be a statistical value or be related to a predetermined target value, calculated, for example, from a target measurement uncertainty.","2":"A typical control chart will consist of a centre line that reflects the level around which the plotted value can be expected to vary. In addition, this control chart will have two lines, called control limits, placed one on each side of the centre line, which define a band within which the value can be expected to lie randomly for a process in a state of statistical control.","3":"Control limits on a Shewhart control chart are placed at a distance of ±2σ and ±3σ where σ is the known or estimated standard deviation of the population. This gives approximate probabilities of 0.05 and 0.003, respectively, of finding values outside the control limits. These limits are known as the upper and lower warning limit (UWL and LWL) and upper and lower action limit (UAL and LAL), respectively. See Shewart means chart - Fig. 1.","4":"A typical response to a value outside a warning limit is to monitor the process and, if this condition is repeated, to stop and investigate.","5":"A value outside an action limit is normally taken as evidence that the process is no longer in statistical control. A typical response to such a value is to stop and investigate. (See process in a state of statistical control)."},"links":[{"term":"Shewhart control chart","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/08125"},{"term":"control chart","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/08068"},{"term":"process in a state of statistical control","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/08099"},{"term":"target measurement uncertainty","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/08133"}],"sources":["PAC, 2021, 93, 997. 'Metrological and quality concepts in analytical chemistry (IUPAC Recommendations 2021)' on page 1023 (https:\/\/doi.org\/10.1515\/pac-2019-0819)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/08069\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/08069\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/08069\/plain"},"citation":"Citation: 'control limit' 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.08069","license":"The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) for individual terms.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.","accessed":"2026-04-18T23:53:49+00:00"}}