Quality engineers use capability (or precision) indices to indicate the extent to which a process or machine can satisfy a specification. Like all other parameter estimates based on sampling. such indices are subject to uncertainty. The paper presents simple but effective approximations for standard errors and confidence intervals for some widely used indices. The presentation covers both American and British/European terminology.

Summary Existing cusum methods are reviewed, and their relevance to quality control problems is considered. Extensions to the techniques are proposed, and tables, nomograms and charts provided to facilitate their application to practical situations.

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SUMMARY The run length properties of Control charts and Cusum schemes, under conditions of slippage in mean level by step‐change to a new sustained level, are well documented. Such control procedures are often used where a genuine “out of control” signal may result from gradual, rather than step, changes. The paper presents the results of evaluation of run length under linear trend for some well‐known procedures.